Table of Contents (click on the link to direct you to the portion of this page with the associated content):

Introduction to Trace Evidence
Contributed by Patrick Buzzini

Textile Fiber Analysis
Contributed by Eileen Davis

Damage to Textiles
Contributed by Sandy Koch

Knot and Ligature Analysis

Contributed by Robert Chisnall

Paint Analysis
Contributed by Scott Ryland
Polymer Analysis
Contributed by Ed Suzuki
Glass Analysis
Contributed by David A. Green

Lubricant Analysis
Contributed by Jeffrey Dake
Explosives Analysis
Contributed by Natasha Neel

Soil Analysis
Contributed by Will Randle

Gunshot Residue (GSR) Analysis
Contributed by Faye Springer

Fire Debris Analysis
Contributed by Michael A. Trimpe; Dana Greely; & Emily Weber

Hair Analysis
Contributed by Amy Michaud
Physical Fit/Fracture Match Analysis
Contributed by Troy Nowak
Tape Analysis
Contributed by Jenny Smith
Building Materials Analysis
Contributed by Bill Schneck

Bank Security Dye Packs/Dye Bomb Analysis
Contributed by Larry Peterson
Glitter Analysis
Contributed by COMING SOON
Lamp Filament Analysis
Contributed by Scott Ryland
Air Bag Analysis
Contributed by Glenn Schubert

Fireworks Analysis
Contributed by Micheal A. Trimpe

Lachrymators/Pepper Spray Analysis
Contributed by COMING SOON
Feather Analysis
Contributed by Marcy Heacker and Carla J. Dove, PhD
Cordage Analysis
Contributed by Karen Lowe
Wood Analysis
Contributed by Michael A. Trimpe

Match Analysis
Contributed by COMING SOON
Cosmetics Analysis
Contributed by COMING SOON

Cigarette Butt Identification Analysis
Contributed by Michelle B. Clarke, Ph.D.

Palynology
Contributed by Vaughn M. Bryant

Footwear and Tire Impression Examinations 
Contributed by Cheryl Lozen

Footwear and Tire Impression Crime Scene Reovery

Contributed by Lesley Hammer

Introduction to Trace Evidence
Contributed by Patrick Buzzini

Department of Forensic Science, Sam Houston State University

Trace evidence is that subdiscipline of criminalistics that is concerned with the recognition, detection, collection, characterization, comparison, and the interpretation of a large array of clue materials.  These materials consist of different types of mass-produced or naturally occurring substances that transfer, often, but not necessarily, in small amounts and sizes during a given activity.  Typical examples of trace evidence are textile fibers, ignitable liquid residue potentially used as accelerants in arson cases, gunshot residue, surface coating (or paint), glass, cosmetics, human and animal hair, soil and minerals, tapes, lamp filaments, explosives, wood chips, botanical substances such as pollen, and much more.

As a corollary it can be stated that “anything can be trace evidence.”  Indeed, a well-known pragmatic definition describes trace evidence as any type of evidence that does not fall into a particular unit or department of a forensic laboratory.  Therefore, trace evidence examiners are the most versatile scientists within a forensic laboratory setting.  As mentioned above, they are confronted with different types of materials.  This clearly evokes the notion of variety.  This notion does not only limit itself to the type of evidence, but also to the variety of sizes of specimens that can be recovered, the variety of their forms, and, as a consequence, to the variety of methods and procedures that are utilized for their collection and examination.

For example, glass fragments can be recovered in large numbers and sizes at accident scenes, or in millimetric sizes on the garments of an individual suspected of having smashed a window; glass particles can also occur in powder form on a bullet having impacted through a window.  Paint can be recovered in the form of multilayered fragments, in the form of abrasions, or in the form of droplets if produced by a spray can.  Textiles can be recovered as individual fibers, but also in the form of yarns (e.g. cordage), or in the form of torn pieces of cloths.  Our environment is extremely rich in the macroscopic and microscopic forms of a large variety of dust particles.  Morphology is one of the main features that a trace evidence examiner exploits particularly using microscopical methods, whether it be light microscopy or electron microscopy.  Gunshot residue, for example, exhibits distinctive spherical shapes, and fibers display different morphological properties depending on their natural or man-made origins.  Ignitable liquid residues are volatile compounds.  The detection of drink adulterants involves the study of liquids.  Physical matches are carried out on fragmented solid debris.

Trace evidence, as vestiges left behind or taken with during activities between individuals or objects follow the same process as any other types of physical evidence.  While the focus of forensic laboratories seems to be confined to testing operations and the delivery of reliable outcomes, the utility of trace evidence to a particular case depends on the entire process that trace evidence undergoes, and on the uncertainties that arise along that process.  This process starts with the generation of traces in their various forms, sizes, and quantities following a particular activity within a particular context.  Depending on their quality and quantity, these remnants produced involuntarily under no controlled conditions and during a unique event constitute what De Forest refers to as an imperfect record.  These traces need to be recognized and their potential relatedness to the case at hand has to be assessed.  This requires a judgment of their relevancy to the case.  In many instances, trace evidence is not immediately recognized at the scene, especially when it occurs in microscopic forms.  This requires a microscopical approach from the part of individuals investigating in the field.  Questions such as “if a suspected activity occurred in a given location and in a given mode, which traces are expected to be transferred and having persisted?” become of the upmost importance to detect trace evidence.

Various methods of collection, that ensure proper preservation, are utilized contingent upon, again, the variety of forms and sizes of the recovered clue materials.  Methods such as taping, scratching, vacuuming, nail clippers, combing, manual picking are applied.  Various containers like paper bags, petri dishes, or metallic paint cans are used.

Depending on the case, trace evidence may be collected along with other types of physical evidence.  Prior to conducting laboratory examinations, it is then advisable to conduct a case assessment to evaluate what the contribution of trace evidence would be in the context of the case at hand.  This is a helpful endeavor to prioritize pertinent examinations and to pre-evaluate the impact of potential analytical outcomes.

From a laboratory standpoint, the characterization of the various materials is carried out my means of microscopical examinations and chemical analyses, often instrumental.  The proper use of light microscopy is a building block for trace evidence examinations.  Using instruments such as the stereomicroscope, the compound microscope or the comparison microscope, the trace evidence examiner shall master different microscopical applications to characterize unknown specimens and to compare them to reference samples or other unknown specimens.  Typical examples of these applications are polarized light microscopy (i.e. double polarization techniques or pleochroïsm), fluorescence microscopy, phase contrast and thermal microscopy, or cross sectioning.  Traditional methods of chemical analysis include Fourier transform infrared (FTIR) spectroscopy, gas chromatography coupled to mass spectrometry (GC-MS), and elemental analysis by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) or X-ray fluorescence (XRF).  Other methods like visible or UV-visible microspectrophotometry (MSP) or the glass refractive index measurement system are also used.  It is important to state that more methods are available to the trace evidence examiner.

Trace evidence examinations are conducted to answer different types of questions.  The interpretation of the forensic findings depends on these questions as well as on the context of the case.  However, the starting point is the characterization of the recovered specimens or identification of unknowns. For example, an examiner may state that particles of lead, barium and antimony were identified on a given surface, which is a characteristic of gunshot residue.  Questions pertaining to false positives may arise at this level.

A traditional question of interest is about the source of the recovered clue materials.  If a suspected source is not available it is possible to develop investigative leads by means of searching reference collections, computerized databases, or conducting manufacturer inquiries.  An example among these possibilities would be the use of the PDQ (Paint Data Query) database to develop a list of potential vehicles from paint chips recovered at a scene of a hit-and-run accident.  Another formidable use of trace evidence would be the comparison between clue materials of a given type recovered at a given scene, and clue materials of the same type recovered at other scenes.  A comparative approach such as this has the potential to help investigators conducting case linkages.  For example, fibers collected from dead bodies recovered at different places and times have been used, in concert with other investigative information, to attribute the homicides to the same individual.  If a putative source is available a comparative examination is typically conducted between recovered specimens and reference samples: the goal would be to explore the possibility to reach a decision of a common source between the compared sets (individualization).  Given the impossibility to reach a decision of source attribution in the most part of cases, an approach would be to evaluate the evidential value based on the evaluation of the rarity of the clue materials in a relevant population or environment.  The more peculiar the observed attributes are, the higher their evidential value.

Other questions such as the occurrence of a particular contact between two surfaces or objects during a well-defined alleged activity may be advanced.  In that case, the presence of the evidence must be explained, rather than their source only.  The trace evidence examiner shall then typically evaluate if the location and the quantity of the recovered clue materials are in agreement with the supposed alleged activity.  Important notions such as transfer, persistence, and evidence recovery efficiency need to be considered.  For example, what would be the expectations to recover a single hair (microscopically indistinguishable from the victim’s hair) in a car trunk for reasons other than transporting a dead body, and given the particular case circumstances?  Finally, trace evidence examinations can play a key role in the reconstructions of incidents (i.e. crimes, suicides or accidents).  They can help the criminalist to understand the relative positions of individuals and objects at the scene, to establish a sequence of events, and to corroborate or infirm claims from victims, suspects, and witnesses.

Additional References:

  1. Locard E. Dust and Its Analysis – An Aid to Criminal Investigation. Police Journal 1928; 177-192.
  2. Palenik S, Palenik C. Microscopy and Microchemistry of Physical Evidence (Ch. 5).  In: Saferstein R (editor).  Forensic Science Handbook – Volume II (2nd edition). Pearson Prentice Hall, Upper Saddle River, NJ (2005): 175-230.
  3. De Forest P. R. What is Trace Evidence? (Ch. 1). In: Caddy B (ed.). Forensic Examination of Glass and Paint – Analysis and Interpretation. Taylor & Francis, London, Philadelphia (2001).
  4. Cook R, Evett IW, Jackson G, Jones PJ, Lambert JA. A Hierarchy of Propositions: Deciding Which Level to Address in Casework. Science & Justice 1998: 38(4): 231-239.

 

Trace Evidence Analysis Disciplines:


Textile Fiber Analysis    
Contributed by Eileen Davis
 

In a forensic context, when referring to this class of evidence one often speaks of the examination of fabric and cordage (e.g. rope, string, twine) as well as the individual fibers that make up these items.  Because textile materials are so prevalent, textile fibers (referred to here as fibers), are a class of physical evidence that may transfer when two persons or a person and an object or location come into contact.  If fibers are recovered from items of evidence, they are examined to determine if a possible association exists between individuals, locations or objects.
If fabric or cordage is involved, an examination will first be conducted to determine if a physical association (also referred to as physical match or physical fit) of a questioned item with a potential source exists.  A physical association is the strongest conclusion possible when referring to fabric or cordage.  If no physical association is possible then a comparison of the fibers composing the fabric or cordage will be conducted as well as an examination of the construction of the items.  Likewise, if individual questioned fibers are recovered and a potential source is available, then a comparison of these fibers to possible source items will be conducted.
Fibers are typically mounted on glass microscope slides and examined using a comparison microscope.  A comparison microscope consists of two compound microscopes joined together by an optical bridge and a single viewing head which presents a side-by-side view of the questioned and known fibers.  Additional microscopic techniques include polarized light microscopy (PLM) and fluorescence microscopy.  Instrumental techniques that also employ a microscope for viewing the fibers include, but are not limited to, Microspectrophotometry (MSP) and Fourier Transform Infrared Spectroscopy (FTIR).
If at the end of all of the examination steps, the known and questioned fibers exhibit no observable differences, then they cannot be eliminated as originating from the same source.  Due to the large production numbers of manufactured textile materials, the comparison of fibers is not a means of positive identification of individual fibers to a specific source.  However, this examination may still provide meaningful information regarding the transfer of fibers.


Additional References:

  1. Forensic Fiber Examination Guidelines, Scientific Working Group for Materials Analysis (SWGMAT), http://www.swgmat.org/

  2. Palenik S. Microscopical examination of fibres. In: Robertson J, Grieve MC, editors. Forensic Examination of Fibres, 2nd edition. London: Francis & Taylor, 1999.

  3. Eyring, M. and Gaudette B. An Introduction to the Forensic Aspects of Textile Fiber Examination. In: Saferstein R, editor. Forensic Science Handbook, Vol. 2. Pearson    Education, Upper Saddle River, NJ, 2005.

 
Damage to Textiles  
Contributed by Sandy Koch
 
A fabric damage analysis starts with characterizing the type of fabric of the textile and combines an analyst’s knowledge of how different weapons or objects typically produce damage with test cuts/punctures/shots made in an undamaged portion of the garment using the suspected weapons.
These tests may provide information either corroborating or refuting a scenario, information about the potential implement that was used to cause the damage and how the damage may have been caused (single insertion, cuts with associated tears, etc). 
Textiles may be woven, knit, nonwoven or a combination of these.  A thorough understanding of how these textiles are constructed and how different weapons affect each particular type of fabric is necessary, especially in cases where a cut/tear crosses a seam.  Test cuts or damage should be conducted during training in order to recognize the variation of damage that may be produced by different weapons as well as through normal wear.  Hospital cuts and scissor stop marks which are typical in gunshot and stabbing cases must be recognized and noted but are generally excluded from a fabric damage examination.
Photography of the item prior to conducting any analyses is necessary in order to provide documentation of the original condition the garment was received in prior to analysis.  Other evidence (hair, blood, paint, etc.) which may require additional analysis should be documented and removed.  The physical damage should be documented prior to conducting test cuts for dimensions (size, length, diameter, etc.) of any damage and the presence of the characteristic V shaped notch indicating a single edged blade
Do not alter the condition of a questioned specimen (e.g., shape, position, layers or relation of one yarn to another) before photographic documentation has been taken.
An evidentiary weapon or other specimen (e.g., a piece of fabric, knife, screwdriver, etc.) should never be brought  in contact with the known fabric from which it is suspected to have originated or damaged until all other forensic analyses (
DNA , latent fingerprints, toolmark analysis, etc) have been performed on the questioned specimen and weapon. 
Cuts and tears in fabrics can offer a great deal of information.  Test cuts may be made with possible weapons to see if they make cuts or tears consistent in the shape and length found on the evidence.  These test cuts should be made in an undamaged portion of the item or if it is too damaged then in a similar type of fabric.  Test surfaces to lay the fabric over can vary between a cardboard box to gel molds to high end body replicas often used in bloodstain analysis.  In addition to comparing the test cuts to cut/tears found in evidence, the relative position of a knife in relation to the cut mark may be determined if a single edged blade was used and the characteristic “v” shaped notch is found at one end of the cut/tear mark.
Weapons should be searched for fibers like the fibers comprising the damaged garments.  Should a fiber association be made, it can strengthen a cut/tear conclusion though the report language for the fabric damage should still be limited to consistent in size and shape with the test cuts and consistent with having been made by that weapon or other implement with similar characteristics (size, shape, sharpness, etc.). 


Additional References:

  1. Kemp, S.E., D.J. Carr, J. Kieser, B.E. Niven and M.C. Taylor “Forensic evidence in apparel fabrics due to stab events” Forensic Science International 191(2009)86-96.

  2. Hearle, J.W.S., Lomas, B., Cooke, W.D. and Duerden, I.J., Fibre failure and wear of materials - An atlas of fracture, fatigue and durability.  New York, NY: John Wiley and Sons, Inc., 1989.

  3. Dictionary of Fiber and Textile Technology. Charlotte, NC: Hoechst-Celanese Corporation.  1990.

  4. Taupin, J.M., F.P. Adolf and J. Robertson “Examination of Damage to Textiles” in Forensic Examination of Fibres 2nd edition.  Edited by J. Robertson and M. Grieve, 1996.

Knot and Ligature Analysis

Contributed by Robert Chisnall

The analysis of knots and rope can be relevant in civil cases, wherein safety equipment has failed resulting in an accident involving injury or death.  The activity under investigation could be recreational (like rock climbing or water skiing for example) or professional (such as construction at height or arborist work).  More frequently, knots and ligatures may have contributed to suspicious deaths and then become a matter of criminal investigation.  Knots are sometimes discovered at a variety crime scenes (including homicide, rape and robbery) and they can become significant pieces of evidence deserving careful preservation, examination and analysis.

During the initial collection and preservation phase, high-contrast photographs of knots in situ must be taken from several different perspectives.  Post mortem and removal procedures must be documented sequentially as well.  Ligatures should be removed by cutting between any knots.  Removal cuts must be subsequently labelled with precision and cut ends should be reconnected if possible using secondary materials.  Reapplying knots and ligatures to mannequins or cardboard forms for storage and presentation can be useful.  Tenuous structures – such as twists, links and loose knots – should be sandwiched between clear packing tape for secure preservation that facilitates ease of analysis.

The observation and data collection phase of the process should take into account the lengths of all cord or rope segments and ends, as well as the circumference of every loop.  An assessment of the relative tightness of each knot should be noted.  (Precise body dimensions can assist in this determination as well.)  The quality of the ends – whether cut, melted or frayed – should be recorded, and the type of tying material employed must be identified.

Most important, the exact structure of each knotted formation, every knot or group of knots, must be carefully identified and described accurately.  An awareness of every subtlety can be critical.  Detailed descriptions should take into account the locations of working ends and standing parts, knot chirality and variations, as well as distortions and capsizements.  Careful drawings must be made to simplify and clarify the relevant detail.  It is often valuable to perform a complete measurement of the ligatures and identification of the knots several times for comparison purposes to eliminate errors.

Repetition can mitigate the chances of missing tangential details, such as biological contamination (blood, semen and saliva, for example) and other trace evidence (hair, paint chips and fibres, for example), which may be trapped within the rope strands or the knots themselves.  Knotted evidence should never be untied, unless there are specific forensic or legal reasons for doing so – such as searching for possible DNA or trace evidence – and that process must be recorded under controlled conditions and only after the knots have be clearly photographed and accurately identified.

A qualitative assessment of the tying sequence must be established.  The examination may reveal whether one or two working ends were employed during the tying process, if external or self-tying occurred, and the purpose of the knots and ligatures found at the scene.  Experimentation with secondary ropes under safe conditions may be required.  The presence of any accidental, residual or capsized knots must be noted.  Most cases present commonplace Overhand Knots, Overhand Loops, Overhand Slip Loops, Reef Knots, Granny Knots, Half Hitches, Half Knots, and clusters of these basic formations.  (The convention is to capitalize knot names.)  Since knotting terminology varies throughout the knotting mainstream literature, and since forensic nomenclature is not consistent globally, the names and labels employed have to be appropriate and unambiguous.

Knot evidence is group characteristic, like blood typing, and individualization is not possible.  It can be corroborative or equivocal, offering several possible explanations.  Qualitative features and certain patterns may suggest self-tying or external tying – thus distinguishing between suicide, homicide and auto-erotic fatalities.  It may be possible to determine the number of tiers, and perhaps the handedness of those tiers, although the research in this regard is currently too limited to allow any statistical claims.  However, there may be progress in this area.

In those rare cases involving more sophisticated knots that require training and experience, certain hobbies or occupations could be suggested.  Knot evidence may provide grounds for search warrants and wire taps in order to acquire further evidence related to suspect knot-tying habits and activities.

Research into tying habits and specific knot morphologies is ongoing.  Relative to other specialties, there is a small but growing body of publications and research pertaining to forensic knot analysis.

Additional References:

Budworth G. Knots and Crime. Great Britain: Police Review Publishing Co. Ltd., 1985.

Chisnall R. The Forensic Analysis of Knots and Ligatures. Salem, Oregon: Lightning Powder Company, Inc, 2000.

Chisnall R. What knots can reveal: the strengths and limitations of forensic knot analysis. Journal of Forensic Identification. 2007, Volume 57, No. 5, pp. 726-49.

Chisnall R. Tying Anomalies and their significance in analysing knot evidence. The Canadian Society of Forensic Science Journal, 2009, Volume 42, No. 3, pp. 172-94.

Chisnall R. Knot-tying habits, tier handedness and experience.  The Journal of Forensic Sciences, 2010, Volume 55, No. 5, pp. 1232-44.

Chisnall, R. Basic principles of forensic knot analysis: a qualitative study of tying behaviour. The Investigative Sciences Journal, 2010, Volume 2,  No. 3, pp. 33-44 investigativesciencesjournal.org/ Nov. 29, 2010.

Chisnall, R. An analysis of more than 100 cases involving knots and ligatures: knot frequencies, consistent tying habits and noteworthy outliers. The Australian Journal of Forensic Sciences. 2011, Volume 43, No. 4, pp. 245-262

Nute, H.D. Mirror images in knots. Journal of Forensic Sciences 1986, Volume 31, No.1, pp. 272-9.


Paint Analysis
Contributed by Scott Ryland
 

Modern paint is a manufactured product typically consisting of a mixture of numerous materials (components). Its most apparent feature is the variety of colors available.  Different paint manufacturers will usually use different components in their products.  Any given manufacturer also offers a variety of grades or types of paint depending on its projected end use or its cost.  These different grades or types also differ in the components or the relative amounts of components put into them.  As such, even for a single layer of paint, there is a tremendous amount of variation from product to product and there are literally thousands of different kinds of paint in our environment.
 

Paint is usually encountered as evidence of association in a cured form often consisting of multiple intact layers, called a paint chip.  It can be found in homicide, assault, vehicular manslaughter, hit-and-run, and burglary investigations, most often involving vehicle paints, architectural paints, or maintenance paints. It is commonly the most chemically complex type of trace evidence encountered. As noted above, each layer of paint in these chips carries the features distinct to that paint; morphological characteristics, organic chemicals and inorganic chemicals.  Obviously, the more layers of paint present in a chip, the less likely it is for one to randomly encounter another source of paint with the same characteristics (layer sequence and individual layer components).The basic thrust of a forensic paint examination is to try to differentiate between paint samples and eliminate the possibility that they have the same source.  The approach uses the scientific method and hypothesis testing. Paint is usually mass-produced using a recipe and sometimes in rather large batches. Accordingly, one has to consider the possibility that a given paint could be applied to a number of different sources.  It is therefore often impossible to definitively associate a given paint sample's origin with one source to the exclusion of all others.  There are exceptions to this, as in the case of paint chips with fractured edges or surface configurations that physically correspond to the paint at the source.


Using established forensic techniques, however, can lead to scientifically based conclusions as to the possibility that given paint samples originated from  the same source. The techniques used in forensic paint comparisons are classical microscopical and analytical instrumental chemistry techniques taught in universities worldwide.  They include such methods as stereomicroscopy, polarized light microscopy (PLM), Fourier Transform infrared microspectroscopy (FTIR), pyrolysis gas chromatography in conjunction with mass spectrometry (PyGC-MS), scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy (SEM-EDS), and UV-Vis microspectrophotometry (MSP). ASTM International has published several consensus guidelines on these topics, to include a Standard Guide for Forensic Paint Analysis and Comparison (ASTM E1610-2014), a Standard Guide for Using Infrared Spectroscopy in Forensic Paint Examinations (ASTM E2937-13), a Standard Guide for Using Scanning Electron Microscopy/X-ray Spectrometry in Forensic Paint Examinations (ASTM E2809-13), and a Standard Guide for Microspectrophotometry and Color Measurement in Forensic Paint Analysis (ASTM E2808-11). In addition, the Scientific Working Group for Materials Analysis has posted a Standard Guide for Using Pyrolysis Gas Chromatography and Pyrolysis Gas Chromatography-Mass Spectrometry in Forensic Paint Examinations on their website (www.swgmat.org).  If one applies to two samples in question a thorough analytical scheme which differentiates between the various physical and chemical features in most paints, one can deduce whether or not they are like one another.  If significant differences are found, the results lead the examiner to the conclusion that the paints are dissimilar and did not originate from  the same source.  If no significant differences are found, the results lead the examiner to the conclusion that the paints are alike in all their measured significant characteristics and that it is possible that they originated from the same source. The evidentiary significance of the correspondence is reflected by the ability of the analytical scheme to differentiate between most paints. This ability can be demonstrated by published discrimination studies.

Additional References:

  1.  Forensic Examination of Glass and Paint: Analysis and Interpretation, B. Caddy, ed., Taylor and Francis, NY, NY, 2001.
  2. Thornton, J., "Forensic Paint Examinations," Chapter 8, in Forensic Science Handbook, Vol. I, 2nd ed., Saferstein, R., ed., 2002, pp. 430-478.
  3. Ryland, S., Jergovich, T. and Kirkbride, P., “Current trends in forensic paint examination,” Forensic Science Review, Vol. 18, No. 2, July 2006, pp. 97-117.
  4. Ryland, S.G. and Suzuki, E.M., “Analysis of Paint Evidence,” Chapter 5, in Forensic Chemistry Handbook, L. Kobilinsky, ed., John Wiley and Sons, Inc., 2012, pp. 131-224.

Case References:
Due to the nature of the cases and the amount of evidence involved, many of the cases involving paint evidence are adjudicated prior to trial.

  1. United States vs. Benjamin Williams and James Williams, CR. No. S-00-139 GEB, United States District Court for the Eastern District of California, domestic terrorism, 2002.
  2. State of Florida vs. Daniel Conahan, Jr., CR No. 97-0166CF, 20th Judicial Circuit, serial homicides, 1996.
  3. State of Alabama vs. Williamson Samual Cecil III, CC 2007 002721 00 W012, in the Circuit Court of Tuscaloosa County, first degree assault and first degree theft, 2010.
  4. State of Florida vs. Jerrold Baron, CR No. 06-418CF, 15th Judicial Circuit, vehicular homicide, 2007.
  5. United States vs. Frankie Maybee, case number 3:11-CR30006-001, United States District Court for the Western District of Arkansas, attempted murder/hate crime, 2011.
  6. State of Florida vs. Ryan Welch, 2012CF2181, Division F, 1st Judicial Circuit, vehicular manslaughter and leaving scene with death, 2013.

 
Polymer Analysis
Contributed by Ed Suzuki

Natural and synthetic polymers are ubiquitous.  Natural organic polymers (cellulose, silk, protein, DNA, chitin, etc.) are predominantly from biological sources, while inorganic ones (quartz, mica, asbestos, etc.) are minerals.  These materials may be analyzed in the forensic science laboratory as they occur as textile fibers; tissues, extracts and residues examined for human or animal DNA; soils; building materials; and other types of evidence.

Modern societies are also heavily dependent on synthetic polymers, which comprise materials such as plastics, rubbers, foams, composites, adhesives, films, tapes, paint binders, and man-made fibers.  This importance is probably best exemplified by a scene from a 1967 popular movie, The Graduate.  In it, Dustin Hoffman plays a listless individual who has just graduated from college.  At his graduation party, he is approached by a guest who counsels him regarding his future job prospects: “I have just one word for you—Plastics.”  The guest was referring, of course, to the increasing prominence that plastics and other synthetic polymers were assuming in our society.  Reflective of this, archeologists of the future are likely to have a very definitive chronological marker when excavating sites: artifacts constructed of synthetic polymers will suddenly become prevalent.    

Because so many everyday objects are constructed of synthetic polymers, it is not surprising that they are frequently encountered as evidence.  Paints, fibers and tapes, discussed elsewhere, are all constructed of polymeric materials—mostly synthetic. A wide variety of other materials comprised of or incorporating synthetic polymers can also be examined as evidence, and their differentiation, identification, and comparison constitute another sub-discipline of trace evidence, usually referred to simply as “Polymer Analysis.”

Like other types of trace evidence examinations, this sub-discipline may entail either an identification of an unknown material or a comparative analysis.  An unknown material is submitted as evidence to determine not only what it is, but more importantly, what significance it might have to the circumstances of the case under investigation.  For an unknown material identified as a synthetic polymer, the type of polymer may provide some clues as to function of the object from which it originated.  However, other properties, such color, size, texture, morphology, and structure (that is, is the material a film or laminate?) can be even more revealing.  A forensic polymer analysis may therefore encompass a variety of examinations in addition to determination of the chemical makeup of the polymer.  As an example, polyurethane foams are very common materials used for a variety of different purposes, but there are two types.  Flexible polyurethane foam (an open cell foam) is used for packaging materials, furniture filling, seat cushions, and carpet underlays; rigid polyurethane foam (a closed cell foam) is used for thermal insulation and floatation devices.  Chemically, both are polyurethanes, but their textures differ and under a microscope, they look as different as night and day: open cell foams are comprised of a network of branching filaments, while closed cell foams are comprised of interlocking miniature compartments.

More often, a comparative analysis is performed to determine if the polymeric materials could share a common origin or otherwise be used to link individuals, events, places, or objects.  For example, an individual suspected of rape is found with a few tiny particles on his shirt.  These are analyzed by a trace analyst, who identifies them as plastic glitter particles.  At the time of the alleged incident, the victim was wearing eye shadow that included glitter particles.  The analyst compares the glitter particles from the suspect’s shirt and from the victim, and finds that they are similar in color, size, shape, thickness, layer structure (each has seven layers), and chemical composition of each layer.  Various commercial glitter particles are known to vary in these properties.  The analyst concludes that the particles found on the suspect could have come from the victim, or some other source that happens to use this same type of glitter particle.  In a real case, it is possible that the glitter particles would also include residue of the eye shadow powder, which could provide further evidence linking the suspect and the victim.

Some of the wide variety of synthetic polymer evidence that may be examined in the forensic science laboratory, as well as the various analytical tools used for their analysis, can be seen from the titles of the six references listed below.

Selected References:

  1. Proceedings of the International Symposium on the Analysis and Identification of Polymers, U.S. Government Printing Office: Washington D.C., 1984.
  2. Shen Z et al. A Case Study on Forensic Polymer Analysis by DIOS-MS: The Suspect Who Gave Us the SLIP®. J Forensic Sci 2004:49:1028-1035.
  3. Vernoud L et al. Characterization of Multilayered Glitter Particles Using Synchrotron FT-IR Microscopy. Forensic Sci Int 2011:210:47-51.
  4. Hashimoto T et al. Morphological and Spectroscopic Measurements of Plastic Bags for the Purpose of Discrimination. J Forensic Sci 2007:52:1082-1088.
  5. Sarkissian G. The Analysis of Tire Rubber Traces Collected After Braking Incidents Using Pyrolysis-Gas Chromatography/Mass Spectrometry. J Forensic Sci 2007:52:1050-1056.
  6. Ihms EC, Brinkman DW. Thermogravimetric Analysis as a Polymer Identification Technique in Forensic Applications. J Forensic Sci 2004:49:505-510.


Glass Analysis     
Contributed by David A. Green

Glass can be found in most localities. It is produced in a wide variety of forms and compositions, and these affect the properties for this material. It can occur as evidence when it is broken during the commission of a crime. Broken glass fragments ranging in size from large pieces to tiny shards may be transferred to and retained by nearby persons or objects. The mere presence of fragment of glass on the clothing or alleged burglar in a case involving entry through a broken window may be significant evidence if fragments are detected. The significance of such evidence will be enhanced if the fragments are determined to be indistinguishable in all measure properties from the broken window.

The raw materials for glass manufacturing are first mixed together to form a batch and then melted in a furnace to produce a liquid. Most modern, commercially produced glass is manufactured in a nonstop process wherein raw materials are fed continuously into one end of a melting tank and liquid glass is drawn from the other end. The composition of the glass changes gradually as more raw materials are added (Arbab 2005).

Although modern glass manufacturing is a highly automated process that produces glass with large scale uniformity, minor variations in the properties of the resulting glass remain. Each of the raw materials used to produce glass contains impurities that are uncontrolled by the manufacturers and consequently vary in amount and composition over time. The mixing of raw materials during batching is incomplete, and the batch will unmix during transport and delivery to the furnace. Some mixing occurs as the molten glass flows through the furnace, but it is not sufficient to make an absolutely uniform product. The refractory material lining the glass furnace is gradually eroded into the glass melt over the lifetime of the furnace. These factors result in glass products with small but measurable variation in their chemical, optical and physical properties both within and between production runs (Koon et al. 2002).

There are several measurable characteristics that may be available for laboratory analysis and comparison between and known and questioned sample. The examiner may attempt to determine if two pieces of glass are a physical match. Only when two or more broken glass fragments physically fit together can it be said that they were once part of the same object.

An examiner may screen through glass samples by comparing color, fluorescence, thickness surface features and curvature of the glass samples. All of these techniques are non-destructive and may produce results sufficient to reach an exclusion without conducting any additional examinations.

An examiner can also measure the optical properties exhibited by a glass fragment. Refractive index is the most commonly measured property in the forensic examination of glass fragments because: (1) precise refractive indices can be measured rapidly on the small fragments typically found in casework (2) It can aid in the characterization of glass and (3) it provides good discrimination potential (Koons et al. 2002).

While there are several methods that can measure this property, the forensic community primarily uses an automated method using a phase-contrast microscope, hot stage and monochromatic light source. ASTM E1967-11a Standard Test Method for the Automated Determination of Refractive Index of Glass Samples Using the Oil Immersion Method and a Phase Contrast Microscope has been published as a standard for this method.  A second, non-automated technique that is utilized by the forensic community is published by the Association of Official Analytical Chemists (AOAC) Method 973.65 which uses a monochromator and hot stage to allow for variation of temperature and wavelength simultaneously.

As previously stated, concentration of trace elements during the manufacturing process may allow for very good discrimination between two glass samples. Many methods have been used for elemental analysis of glass which include scanning electron microscopy-energy dispersive spectrometry and X-Ray Fluorescence Spectroscopy. ASTM E2926-13 Standard Test Method for Forensic Comparison of Glass Using Micro X-ray Fluorescence (u-XRF) Spectrometry has recently been published.

The most discriminating analytical method for glass fragment comparisons can be accomplished utilizing inductively coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS). Currently there are two ASTM standards with regard to ICP-MS analysis, ASTM E2330-12 Standard Test Method for Determination of Concentrations of Elements in Glass Samples Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for Forensic Comparisons and ASTM E2927-13 Standard Test Method for Determination of Trace Elements in Soda-Lime Glass Samples Using Laser Ablation Inductively Coupled Plasma Mass Spectrometry for Forensic Comparisons.

When no differences within the limits of the analytical techniques of the assessed properties can be identified, the possibility that the glass fragments originated from the same source cannot be eliminated.

In addition to above listed ASTM standards for glass analysis, the Scientific Working Group for Material Analysis (SWGMAT) has produced guideline documents for glass analysis, which include, Elemental Analysis of Glass, Glass Density Determination, Glass Fractures, Glass Refractive Index Determination, and Initial Examinations of Glass, all of which can be found at the FBI online publication Forensic Science Communications.

Additional References:

Arbab, M., Shelestak, L. J., and Harris, C. S. Value-added flat-glass products for the building, transportation markets, part 1, American Ceramic Society Bulletin (2005) 84:30–35.

Bottrell, M. Forensic Glass Comparison: Background Information Used in Data Interpretation, Forensic Science Communication [Online]. (April 2009). Available: http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/april2009/review/2009_04_review01.htm/.

Koons, R. D., Buscaglia, J., Bottrell, M., and Miller, E. T. Forensic glass comparisons. In: Forensic Science Handbook. Vol. I, 2nd ed. Richard Saferstein, Ed., Prentice Hall, Upper Saddle River, New Jersey, 2002, pp. 161–213.

Scientific Working Group for Materials Analysis (SWGMAT). Elemental analysis of glass, Forensic Science Communications [Online]. (January 2005a). Available: http://www.fbi.gov/hq/lab/fsc/backissu/jan2005/standards/2005standards10.htm. References reprinted at .http://www.fbi.gov/hq/lab/fsc/backissu/jan2006/standards/2006_01_standards05.htm.

Scientific Working Group for Materials Analysis (SWGMAT). Glass density determination, Forensic Science Communications [Online]. (January 2005b). Available: http://www.fbi.gov/hq/lab/fsc/backissu/jan2005/standards/2005standards8.htm. References reprinted at http://www.fbi.gov/hq/lab/fsc/backissu/jan2006/standards/2006_01_standards03.htm.

Scientific Working Group for Materials Analysis (SWGMAT). Glass fractures, Forensic Science Communications [Online]. (January 2005c). Available: http://www.fbi.gov/hq/lab/fsc/backissu/jan2005/standards/2005standards7.htm. Bibliography reprinted at http://www.fbi.gov/hq/lab/fsc/backissu/jan2006/standards/2006_01_standards02.htm.

Scientific Working Group for Materials Analysis (SWGMAT). Glass refractive index determination, Forensic Science Communications [Online]. (January 2005d). Available: http://www.fbi.gov/hq/lab/fsc/backissu/jan2005/standards/2005standards9.htm. References and bibliography reprinted at http://www.fbi.gov/hq/lab/fsc/backissu/jan2006/standards/2006_01_standards04.htm.

Scientific Working Group for Materials Analysis (SWGMAT). Initial examination of glass, Forensic Science Communicationshttp://www.fbi.gov/hq/lab/fsc/backissu/jan2005/standards/2005standards6.htm. Bibliography reprinted at http://www.fbi.gov/hq/lab/fsc/backissu/jan2006/standards/2006_01_standards01.htm. [Online]. (January 2005e). Available:
 
Lubricant Analysis  
Contributed by Jeffrey Dake
 
Condom lubricants, commercial sexual lubricants and improvised lubricants may be of evidentiary value in criminal casework, particularly in sexual assault cases.  Residues from these products may be found and collected from bodily swabs (vaginal, penile, etc.), intimate items of the involved parties, and/or bedding.  The materials found in these residues can be compared to the composition of condom lubricants and/or sexual lubricants suspected to have been used to facilitate a sexual act. 
Condom lubricants and sexual lubricants typically consist of base lubricants, which may be water soluble or water insoluble in nature.  Additionally, these types of products may contain additives in order to achieve a functional end (such as the addition of a spermicide, a flavoring, or a desensitizing agent), to act as a preservative, or as a by-product of the manufacturing process.  A variety of instrumental techniques may be employed in the analysis of lubricant materials including, but not limited to microscopy, Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. 
The presence or absence of materials associated with lubricants may help to corroborate or refute a party’s account of the events.  Additionally, as condoms are a barrier method for preventing pregnancy and the transmission of sexually transmitted diseases, their use in a sexual assault may prevent the transfer of DNA evidence.  As such, the presence of materials associated with condom residues may be the most probative evidence in these types of offenses.


Additional References:

  1. Blackledge, R. D., Vincenti, M., “Identification of Polydimethylsiloxane Lubricant Traces from Latex Condoms in Cases of Sexual Assault”, JFSS, 34 (4), PP. 245-256, 1994.

  2. P. Maynard, K. Allwell , C. Roux, M. Dawson, D. Royds, “A Protocol for the Forensic Analysis of Condom and Personal Lubricants Found in Sexual Assault Cases”, FSI, 124 (2001), PP. 140-156.

  3. Keil, Wolfgang, “Condom Trace Evidence in Sexual Assaults: Recovery and Characterization”, Forensic Analysis on the Cutting Edge, Edited by Blackledge, John Wiley and Sons, 2007.  PP. 81-111.

  4. G.P. Campbell, A.L. Gordon, “Analysis of Condom Lubricants for Forensic Casework”, J. Forensic Sci., Vol. 52, No. 3, May 2007, PP. 630-642.

 
Explosives Analysis  
Contributed by Natasha Neel

The analysis of explosives involves identifying the type of explosive(s) used in a device, or recovered in bulk. Explosives fall into two categories – high explosives and low explosives. The main difference between these two categories is the velocity of detonation. High explosives detonate at a rate greater than the speed of sound whereas low explosives deflagrate. Deflagration involves particle to particle burning. Low explosives usually require confinement to function properly, as opposed to high explosives which do not need to be confined. Low explosives include materials such as: black powder, smokeless powder, flash powder, and black powder substitutes such as Hodgdon® Pyrodex® and Hodgdon® Triple Seven®. High explosives include materials such as: RDX, PETN, TNT, HMX, TATP, HMTD, emulsions, and water gels. 

The analysis of explosives depends on whether or not a sample is received intact or post-blast. More information can usually be derived from a sample that is submitted intact versus a post-blast sample. For example, if an intact sample of smokeless powder is received, an examiner can report morphological and chemical characteristics, for example, that a disc shaped double base smokeless powder was identified. However, if no intact particles are received or recovered during analysis, one may only be able to report that nitroglycerin, a component of double base smokeless powder and some dynamites, was identified.

Analysis of explosives evidence starts by examining the evidence visually and with a stereomicroscope to determine the physical characteristics of the material. As the examiner proceeds with their analysis, the instrumentation and analysis scheme used depends on whether the evidence received is intact or post-blast, and whether the explosives are organic or inorganic. If an intact sample is recovered, the morphology of the material will provide information as to what it may be. An ignition susceptibility test (IST) will also give useful burn properties of the material. With post-blast debris, microscopic analysis is a very important step in the analytical scheme. If the filler used was a low explosive, in most instances intact explosive particles will have survived the blast. The materials that may be available for analysis are dependent on the thoroughness of the evidence collection at the scene, as well as on the manner in which the original device functioned. If no intact particles are recovered, analyzing organic and/or aqueous extracts of the remaining post-blast components and debris will be required. The techniques used for the analysis of explosives and their residues may include FTIR (Fourier Transform Infrared Spectrometry), XRF (X-ray Fluorescence), XRD (X-ray Diffractometry), GC/MS (Gas Chromatography/ Mass Spectrometry), IC/MS (Ion Chromatography/ Mass Spectrometry) , HPLC (High Performance Liquid Chromatography) , LC/MS (Liquid Chromatography/ Mass Spectrometry), and PLM (Polarized Light Microscopy).

In addition to identifying the type of explosive(s) used in a device, another key part in the analysis of explosives evidence is the identification of components involved in the construction/manufacturing of a device. This includes not only the container and shrapnel used, but also any components involved in the firing train such as: fuses, detonators, wires, batteries, switches, and timing mechanisms. Information gathered from component identification is critical to determine where items may have been purchased, to help link devices together, or to aid the investigator during subsequent searches.


Additional References:

  1. Akhavan, J. (2011). The Chemistry of Explosives, (3rd edition). Cambridge, UK: The Royal Society of Chemistry.
  2. Beveridge, A. (Editor).  (2012). Forensic Investigation of Explosions, (2nd edition). Boca Raton, FL: CRC Press.
  3. Conkling, J. & Mocella, C. (2011). Chemistry of Pyrotechnics: Basic Principles and Theories (2nd edition). Boca Raton, FL: CRC Press.
  4. Davis, T. The Chemistry of Powder and Explosives, (reprint edition). Las Vegas, NV: Angriff Press.
     

Soil Analysis 
Contributed by Will Randle

Soil is one of the earliest types of trace evidence to be used in criminal cases.  Unfortunately, today it seems to be an often overlooked piece of evidence.  However, when recognized and collected, its use as class evidence can provide valuable links between victims, suspects and/or crime scenes.  Soils exhibit a wide range of characteristics useful for comparison that depend on the geological & environmental histories as well as human activities at each particular location.  The first known case where soil was used in helping solve a crime was in 1904 when German scientist Georg Popp examined soil collected from the trousers of a murder suspect.  Two distinct soil samples from the trousers were collected.  One sample was consistent in mineral composition to soil from where the homicide victim was found.  The second soil sample was consistent with soil collected from the pathway that connected the crime scene to the suspect’s home.  When shown how the soil evidence tied him to the murder, the suspect confessed.

Soils can consist of minerals, vegetation and man-made materials.  Trace examiners typically study and compare the mineral portions along with any man-made materials such as glass, paint and building materials.   Soils are compared using color, size distribution and mineral composition.  Color is assessed visually using dried soil samples.  The color of each soil can be characterized using Munsell Color Charts.  When the samples are adequate in size, they are sieved using a series of metal screens of known mesh size; each successive sieve is smaller than the sieve above it.  Each sample than is separated into 3 or 4 sized fractions.  The fractions are than weighed and the percent weight of each fraction calculated and compared.  Soils from the same location will show similar size fractions unless the questioned soil sample lost some of its original components.  The next step of the comparison is the examination and comparison of the mineral make-up of the soils.  The minerals contained in 100 or 150 mesh sieved fraction are used for the mineralogical study.  Heavy minerals, such as zircon, epidote, hornblende, garnet and many others, are frequently used for the comparison as they exhibit greater diversity and are more likely to vary between soils from different locations.  Lighter minerals such as quartz and feldspars are common in soils and are less useful in differentiating soils.  The heavy minerals can be separated by adding the sieved soil to bromoform.  The heavy minerals will sink and the light minerals will float.  The collected heavy minerals are then examined using the polarized light microscope.  The various minerals are counted as to the types present.  Soils of the same location will exhibit similar mineral profiles.

Other methods of soil comparisons are currently being explored.  Newer techniques include liquid chromatography, mineral examinations using automated SEM/EDS analysis and biological methods using bacterial DNA.

Additional References:

Murry, Raymond C.  2004. Evidence from the Earth - Forensic Geology and Criminal Investigation, Mountain Press Publishing Company, Missoula, Montana.

McCrone, Walter C. “Forensic Soil Examination,” Microscope Vol 40 pp 109 - 121, 1992

Graves, W.J., “A Mineralogical Soil Classification Technique for the Forensic Scientist,” JFS 24(2) pp 323-338, 1979.

A photomicrograph of various heavy minerals.

 
Gunshot Residue (GSR) Analysis  
Contributed by Faye Springer

Gunshot residue analysis refers to the chemical analysis of particulate materials resulting from the discharge of a cartridge in a firearm.  In its broadest definition, the analysis of GSR includes the identification or characterization of gunpowder, products of gunpowder combustion, primer mixture components, metallic residues from the projectile and cartridge case, and possibly chemical residues from the firearm itself.  However, more commonly, gunshot residue (GSR) analysis refers to the analysis of residue on the hands of a shooter or other surfaces in the vicinity of a discharging firearm.  Most of these analyses specifically target residues resulting from the detonation of the primer mixture inside the primer cup of a round of ammunition, or cartridge.

GSR is typically collected from the hands of a suspected shooter, or from other objects, on adhesive lifts intended for examination by a scanning electron microscope with an energy dispersive spectrometer (SEM/EDS).  Gunshot residue using SEM/EDS is based on original research published by G. M. Wolton of Aerospace Corporation in 1977. 1, 2, 3

Subsequently, forensic laboratories started applying this technology to case work.  In 1994, a standardized method for the analysis of GSR by SEM/EDS was published by the American Society for Testing and Materials (ASTM) as Standard E15884.

In 2005, a scientific working group on gunshot residue (SWGGSR) was formed with representatives from the international forensic GSR community.  The goal of this group was to the develop guidelines for forensic GSR analyses and guidelines for reporting practices.  It also provides a platform for exchanging information concerning current issues in GSR.  This group’s publications can be found on their website at www.swggsr.org/‎.

GSR particles are most commonly characterized by their shape and chemical composition.  Because the particles are formed by the cooling of the molten particles created during the discharge of a cartridge, they tend to be micron or submicron sized particles and somewhat spherical or rounded in appearance.  The most common primer mixture consists of lead styphnate as an initiating explosive, barium nitrate as an oxidizer, and antimony sulfide as a fuel.  Therefore, the presence of these elements in a spherical or somewhat rounded particle is defined as a characteristic gunshot residue particle.

With lead free primers or ammunition becoming more popular, other chemical components may be present in primer mixtures.  The Guide for Primer Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectrometry 11-29-114 published on the SWGGSR website has more information on residue from these types of ammunition.

The presence of characteristic GSR particles on a subject’s hand typically leads to the conclusion that this person:

  • discharged a firearm,

  • was near a firearm when it was discharged,

  • or handled a firearm or another object contaminated with gunshot primer residue.

The lack of GSR particles on the hands of a subject typically means that:

  • the subject did not discharge a firearm,

  • the weapon or ammunition used in this case does not deposit detectable GSR based on current technology,

  • or previously existing GSR deposits on the person’s hands were removed by washing or other mechanical means over time.

Gunshot residue analysis can be expected to change as materials used in the manufacture of ammunition and firearms changes.  In addition, newer generation instrumentation that offers increased sensitivity, specificity, and speed can be expected to influence current procedures and techniques used in the detection of GSR.

Additional References:

  1. Wolten, G. M., Nesbitt, R. S., Calloway, A. R. Loper, G. L., and Jones, P. F., Particle Analysis for the Detection of Gunshot Residue, I: Scanning Electron Microscopy/Energy Dispersive X-ray Characterization of Hand Deposits from Firing. Journal of Forensic Sciences (1979): 409-422.

  2. Wolten, G. M., Nesbitt, R. S., Calloway, A. R. Loper, G. L., and Jones, P. F., Particle Analysis for the Detection of Gunshot Residue II: Occupational and Environmental Particles. Journal of Forensic Sciences (1979): 423-430.

  3. Wolten, G. M., Nesbitt, R. S., Calloway, A. R. Loper, G. L., and Jones, P. F., Particle Analysis for the Detection of Gunshot Residue III: Case Record.  Journal of Forensic Sciences (1979): 864-869.

  4. ASTM Standard E1588-10e1, Standard Guide for Gunshot Residue Analysis by Scanning Electron Microscopy/ Energy Dispersive X-ray Spectrometry.

  5. Guide for Primer Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectrometry 11-29-11, www.swggsr.org/‎.

Fire Debris Analysis
Contributed by 
Michael A. Trimpe; Dana Greely; & Emily Weber

Fire investigators search a fire scene to determine the cause and origin of a fire.  If the cause of the fire appears suspicious the investigators may collect debris from the origin of the fire for analysis in the forensic laboratory.  The debris is typically porous material in which an ignitable liquid could penetrate and remain even after an intense fire. Ignitable liquids are mixtures of volatile chemicals usually distilled from petroleum.  Due to their volatility, ignitable liquids can easily evaporate. Therefore, samples must be collected in airtight containers for submission to the laboratory.

The forensic analyst carefully extracts the vapors from the container and concentrates them in a way that can be analyzed by gas chromatography and mass spectrometry. The gas chromatograph separates the chemicals into a pattern that can be compared to known ignitable liquid standards.  The mass spectrometer allows for identification of the individual chemicals within the mixture.  These techniques and instrumentation are very sensitive and can detect vapors of ignitable liquids that may not even be detected by the human olfactory senses. The technique also allows for an experienced analyst to differentiate between ignitable liquids and the matrix materials often present in fire debris samples.

Fig. 1 Gas chromatogram of a fire debris sample overlaid with a known gasoline standard.

Additional References:

  1. NFPA 921: Guide for Fire and Explosion Investigations, National Fire Protection Association, Quincy MA, current edition
  2. Kirk’s Fire Investigation, DeHaan, John, Brady Publishing, Prentice-Hall, 5th Edition, 2002, ISBN: 0-13-060458-5
  3. ASTM E 1412-12, “Standard Practice for Separation of Ignitable Liquid Residues from Fire Debris Samples by Passive Headspace Concentration With Activated Charcoal,” ASTM International.
  4. ASTM E 1618.,Standard Guide for Identification of Ignitable Liquid Residues in Extracts from Fire Debris Samples by Gas Chromatography-Mass Spectrometry
  5. GC-MS Guide to Ignitable Liquids, Newman, R., Gilbert, M., Lothridge, K., CRC Press, 1998.
  6. Microbial Degradation of Gasoline in Soil, Mann, D.C., Gresham, W.R., Journal of Forensic Sciences, Vol. 35 (4), pages 913-923, 1989.
  7. Turpentine in Arson Analysis, Trimpe, M.A., Journal of Forensic Sciences, Vol. 36 (4), pages 1059-1073, 1991.
  8. The Petroleum-Laced Background, J.J. Lentini, J.A. Dolan, and C. Cherry, Journal of Forensic Sciences, 45 (5), pages 968-989, 2000.
  9. Standard Guide for Fire Debris Report Writing http://swgfex.org/Report_Writing_Guide_SWGFEX.pdf

 
Hair Analysis
Contributed by Amy Michaud
 
Hair evidence is frequently encountered in criminal investigations because hairs are readily lost from both victims and suspects during criminal activity.  Hairs are easily transferred, easily detected and recovered, and are very durable.  Most importantly, hair evidence can supply investigative leads and provide associations between individuals and items involved with a crime.
 
Forensic hair examinations and comparisons are not new or novel.  In fact, this discipline is grounded in comparative biology, microscopy, anatomy, histology, and anthropology and microscopical hair examination has been relied upon for the past 100 years to provide possible associations or exclusions between a recovered hair and known sources of hair. 
 
Any hair examination should start with the use of a good quality high powered microscope.  The microscopical analysis of these hairs can provide investigative information such as the racial characteristics of the hair donor, the likely somatic origin of the hair (e.g. head, pubic, facial, body or limb), the growth phase of the root, and the presence or absence of artificial treatment, damage, or disease to the hair.  Some of these features can aid in providing a physical description of a suspect and others can provide reconstructive information concerning certain activities that may have occurred during the commission of the crime. 
 
If known hairs are available from the victim or suspect, a microscopical comparison can be made using a comparison microscope. Generally, only head and pubic hairs possess sufficient microscopical characteristics for a microscopical hair comparison. This comparison may be used to provide a possible association between the individuals involved in a crime to the crime scene or to each other.  This is possible because the microscopical characteristics observed in the hair of one individual are usually very different from those observed in the hair of another individual.  This is due to the fact that the biological processes vary from one person to another but also because the individual's environment (e.g. diet, chemical treatment or damage to the hair, UV exposure) will create extra dimensions that are useful for comparison. That being said, microscopical hair examination alone cannot conclusively determine if a questioned hair came from a particular individual.  It is possible for two individuals to exhibit similar microscopic characteristics in their hairs, particularly if the hairs have limited microscopic properties as may be the case with some very light colored or gray hairs, very dark opaque hairs, or very short or fine hairs. 
 
Once the microscopical comparison of the hairs is completed, a microscopical examination of the hair root will assess the potential for DNA analysis.  Hairs will commonly lend themselves to either mitochondrial DNA (mtDNA) analysis or, if enough root tissue is present, to nuclear DNA (nDNA) analysis.
 
If nDNA analysis is successful, the profile can be compared to a known nDNA sample from a suspect or victim and provide a near certain association to a single person (with the exception of identical twins).
Additionally, if no suspects have been developed, the profile can be searched in the Combined DNA Indexing System (CODIS) in an effort to identify the individual that the hair originated from. With regards to the limitations of nDNA, it can only provide identity of the individual the hair came from, but cannot provide information regarding the circumstances of the crime (e.g. if it is a head or pubic hair, if it has naturally fallen out or been forcefully removed, if the root is decomposed indicating it came from a deceased individual). Additionally, the overwhelming majority of hairs found in forensic casework do not possess enough tissue to conduct nDNA analysis.
 
When nDNA is not possible, mtDNA analysis is often successful.  While mtDNA cannot be used to unequivocally identify an individual, it can be used to exclude a large portion of the population as a possible donor of the hair and thereby provide very probative evidence.  As with nDNA, mtDNA primarily provides information with regards to the identity of the hair donor and does not provide additional information to help reconstruct the crime. 
 
The combination of microscopical hair comparison and nDNA or mtDNA analysis provides the criminal justice system with significantly more probative information than any of these techniques do alone.
Microscopical comparisons and DNA analysis should always be considered in any case where hair evidence is important. 


Additional References:

  1. Bisbing, RE. The forensic identification and association of human hair. In: Saferstein, R, editor. Forensic science handbook. Volume I.  2nd Ed. New Jersery: Prentice Hall, 2002;389-428.

  2. Scientific working group on materials analysis. Human hair examination guidelines. Forensic science communications 2005; 7(2).

  3. Taupin JM. Forensic hair morphology comparison-a dying art or junk science? Science & Justice 2004; 44(2):95-100.

  4. Robertson J, editor. Forensic examination of hair. London: Taylor & Francis, 1999 6. Ogle RR, Fox MJ.

  5. Atlas of human hair microscopic characteristics. Boca Raton: CRC Press, 1999.

  6. Scientific Working Group on Materials Analysis (SWGMAT) Position on Hair Evidence, Journal of Forensic Sciences, 2009 Vol. 54(5)

Case References:
The microscopical examination and comparison of hairs has been upheld in Daubert hearings in courts in the United States.  Expert testimony supporting hair examinations has been accepted in state and in federal courts throughout the United States and its territories.  While there have been numerous cases in which expert testimony was provided, the following list of court cases includes those cases where the examination and comparison of hairs has been upheld in Daubert hearings and/or where the examination and comparison of hairs provided  significant information to the case:

  1. State of North Carolina vs. Andre Jaren Edwards, 2001 - Ginger

Lynn Hayes and her eleven month old son were abducted while making a stop at a CVS drug store in Greenville, North Carolina.  Hours later, Ginger's body was found near her son who was alive but suffering from exposure.  They were discovered in a field along with several abandoned tires.  Numerous head hairs adhered to the rim of one of those tires were found to be microscopically consistent to the head hair sample from Ginger Hayes.  The hairs on the tire had been crushed and broken, indicating the tire may have been used as the murder weapon.  An autopsy revealed that blunt force trauma to the head resulted in Ms. Hayes' death.   Testimony regarding the damage to the hairs was provided in federal court.

  1. State of Vermont vs. Alfred Brochu, 2004 - This case involved

the rape and homicide of Tara Stratton.  The victim was the girlfriend of Alfred Brochu's son.  Brochu claimed that he was at work on the night of the murder and that he could not have killed her.  Pubic hairs microscopically consistent with the known pubic hair sample from Brochu were found in the body bag that the victim was placed in and at the scene.  Mitochondrial DNA examinations were conducted on these hairs and supported the microscopical examination results.  A Daubert hearing challenging microscopical hair examination was conducted.  The judge ruled that microscopical hair examinations are admissible.  Testimony regarding the hair examinations and conclusions was provided as was testimony regarding the mitochondrial DNA examinations.  Brochu was convicted on all charges.

  1. State of Florida v. Joseph Smith, 2005 - Eleven year old Carlie

Brucia was abducted from outside a carwash in Sarasota, FL in the early evening of February 1, 2004.  Her body was found four days later in a church parking lot.  The abduction was caught on a security camera at the car wash.  The video was broadcast nationally and led to multiple tips eventually identifying Joseph Smith as the suspect.  A vehicle that had been borrowed by Smith was located and processed for evidence.
Several Caucasian head hairs were found on items from the vehicle that were microscopically consistent with originating from the victim.
Additionally, multiple fiber associations were found between the victim's shirt and items recovered from the vehicle. In November 2005, testimony was provided regarding the hair and fiber evidence.  Joseph Smith was convicted on all counts on November 17, 2005 and was sentenced to death.  The death sentence was upheld by the judge in March 2006.

  1. State of New York vs. Arial Menendez, 2006 - Elizabeth Butler, a

teenager, was allegedly raped and killed in her car at a train station.
A pubic region hair was found on the victim's shirt which was microscopically similar to the pubic hair sample from Arial Menendez, her former boyfriend.  A forcibly removed head hair which did not contain follicular tissue was found on the suspect's shirt.  This hair was microscopically consistent with the known head hair sample from the victim.  Both hairs were submitted for mitochondrial DNA examinations with those results supporting the microscopical hair conclusions. Testimony was provided by both the hair examiner and the mtDNA examiner regarding these results.  Menendez was convicted of all charges.

  1. State of New York vs. Anne Trovato, 2006 - Patricia Mery was

found deceased after being stabbed multiple times and beaten with a bat.
Cell phone records placed her estranged daughter, Anne Trovato, near the crime scene.  Two head hairs on a knife found at the crime scene were compared to known head hair samples from the victim and her daughter.
These hairs had no apparent tissue and accordingly were only suitable for mitochondrial DNA analysis.  Since Patricia Mery and Anne Trovato were maternally related, mitochondrial DNA results included both the subject and the victim as possible donors of the hairs.  Prior microscopical examination of the hairs however, concluded that the hairs from the knife were not consistent with originating from the victim but that they could not be excluded as having originated from the suspect.  Hair and mtDNA examiners testified in October, 2007 and Trovato was convicted.

Physical Fit/ Fracture Match Analysis
Contributed by Troy Nowak

Fracture match examinations are conducted to show the realignment of two or more objects to prove that they at one time formed a single object.

There are several types of materials fracture match examinations can be useful in:

  • Glass (in a breaking and entering)
  • Metal (forced entry with a tool)                                                                        
  • Wood (assault with baseball bat)                                                   
  • Plastic materials (to include wrappers, bags, etc)
  • Paint (hit and run)
  • Tape (binding)

                                                                                         

Certain criteria must be met for fracture match examinations to be conducted.  Obviously the item(s) must be broken and detached, then the items must be capable of being physically realigned (perhaps a portion is missing, can it be found), do the items fit together as a “lock and key” like a jigsaw puzzle (surface markings may exist on the item that align and look for an edge to edge boarder), and are the pieces unique (can they be interchanged with similar pieces elsewhere).

There are 3 dimensions (depth and edges) to a separation; each dimension of the separation should be examined.

Class and individual characteristics must be observed for a conclusion to be drawn in a fracture match examination and the examiner must be familiar with class and individual characteristics:

  • Class Characteristics are those characteristics that make items similar at best – for example, color, shape, pattern.  Measurable features of a specimen resulting from design factors, these are determined prior to manufacture.
  • Individual Characteristics are those characteristics that make items unique – for example, accidental surface markings due to wear or use.  In an uncontrolled environment, the physics (torque, acceleration, force, speed) behind the random force used to break or tear an item are not reproducible.

Why conduct a fracture match examination?  These types of examination can be a positive form of identification.  One item can be associated to another item to the exclusion of all others; meaning that an item did not originate from any other source.

So what differentiates a skilled forensic examiner from the casual observer?  One must have experience, the ability to recognize the criteria for a fracture match, the ability to distinguish between class and individual characteristics, and an understanding of the scientific method.

Tape Analysis     
Contributed by Jenny Smith
 
Tape products often become items of evidence for the trace evidence chemist.  Criminals find tape; particularly duct tape, useful for ligatures, gags, and restraints and to wrap up improvised explosive devices and drugs.  A questioned tape end can be physically matched to a known roll of tape to give individualizing evidence or can be associated by class characteristics.  The tape itself can bare fingerprints or saliva (DNA) when cut with the teeth and often trace evidence such as hair and fibers may be caught in the adhesive.  As with many commercial products that trace evidence chemists are asked to compare, it is important first to establish the variability of the product in order to assess its significance. 
Duct tape is made up of as many as 50 chemical components; plastics, rubbers, fillers, stabilizers, tackifiers, colorants, etc.  Each of these are subject to market fluctations and are frequently changed.  Herein lies the variability.  In fact, duct tape has been found to be variable between manufacturers, within the same manufacturers and even within the same batch of tape. The comparison of duct tape by a trace analyst will involve the use of polarized light microscopy, infra-red spectroscopy and elemental analysis encompassing most of the skills of the analyst.  
Because of this changing market, tape products can provide useful investigative leads and should always be collected from the scene of a crime.
 


Building Materials Analysis
Contributed by Bill Schneck
 
Transfer of building materials between individuals, tools, and weapons may occur during the commission of practically any crime.  Building materials encountered in casework include friable insulation products, hardened concrete, gypsum-containing plasters, glass, safe insulation, asbestos, paint, wood and engineered wood products and materials which are pliable, soft and easily transferred.
Building materials may transfer to a suspects clothing and hair during a burglary. Particles on discharged bullets can help determine trajectory by defining which wall the bullet traveled through.  Tools found in a suspect’s possession may have attached building materials which could offer important clues in an investigation. Motor vehicles involved in an accident may be an excellent repository of building materials from contact with an immovable object such as a concrete barrier or wooden utility pole.  Civil litigation may involve an expert’s testimony on asbestos-containing building materials which can often be identified to the manufacturer. Traces of concrete, brick, glass fibers and sawdust can be found reworked into soil and are often encountered as evidence.
The analytical methods employed in the analysis of building materials include polarized light microscopy, micro-chemical tests, infra-red spectroscopy, scanning electron microscopy-energy dispersive spectroscopy and other tools such as x-ray diffraction.

Additional References:

  1. ASTM Designation: C 856-95, Standard Practice for Petrographic Examination of Hardened  Concrete.

  2. Bisbing, R. E. and Schneck, W. M., Particle Analysis in Forensic Science, Forensic Science Review, 18(2), July, 2006.

  3. Brown, R. S., Boltin, W. R., Bandli, B. R., Millette, J. R., Light and Electron Microscopy of Mineral Wool Fibers, Microscope, Vol 55:1, p. 37-44, 2007.

  4. Campbell, D. H., Microscopical Examination and Interpretation of Portland Cement and Clinker, Portland Cement Association, Skokie, IL., USA, 1999.

  5. Carr, D. D., Industrial Minerals and Rocks, 6th Edition, Society of Mining, Metallurgy, and Exploration, Littleton, Colorado, 1994.

  6. Double, D. D., and Hellawell, A., The Solidification of Concrete, Scientific American, pp. 82-90, July, 1977.

  7. Hoadley, R. B., Identifying Wood –Accurate Results with Simple Tools, Taunton Press, Newton, CT, 1990.

  8. McCrone, W. C., Asbestos Identification, McCrone Research Institute, Chicago, Illinois, 1987.

Case References:

  1. A boy was sexually assaulted on a baseball field in southern California. The physical evidence left at the scene included several poorly preserved shoe impressions with insufficient marks to identify the brand of shoes.  A suspect was arrested and his shoes were examined for trace evidence.  Small red brick particles were identified in the soil.  Investigations determined the material used for the baseball infield was recycled red brick.  Microscopical and instrumental analysis confirmed the red brick on the suspect’s shoes was similar to the red brick used at the baseball field.  The suspect pled to the crime (Figure 1a- 1b).

  2. A body was found lodged in the back seat of a minivan parked along a street.   Soil was observed clinging to the wheel wells of the vehicle.  Examination of this soil and comparison soil from the driveway of a run-down dwelling in a distant location revealed similar minerals and botanicals.  Mixed in the soils from both the vehicle and the driveway were a variety of red, green, white and gray particles, some with adhering asphalt and fiberglass.  The duplex adjacent to the driveway lacked rain gutters.  Over time, decaying asphalt roofing granules fell from the roof and mixed with the soil.  This unusual association of building materials in soil proved useful to the prosecution of the homicide (Figure 2a-2b).

  3. The body of a female victim was found tied up in agricultural sacking and covered with stones and tabular concrete slabs on a ledge adjacent to a river in Ireland.  The suspect lived 100 meters from the covert burial.  Concrete slabs in the suspect’s garden with similar features were compared to the concrete from the burial site.  Methods employed included hand specimen, cut section and petrographic examination of concrete thin-sections, x-ray fluorescence analysis, and disaggregation of concrete in acid which enabled automated particle size analysis of the sieved aggregate. The comparison of the concrete was instrumental in the conviction of the suspect to life in prison without parole. (Figure 3).

DSCN5545     DSCN5554
Figure 1a. Soil from baseball field            Fig 1b.Red brick particles in soil from suspect shoe
 
        
       Figure 2a. Polished section of asphalt roofing grains
 
      
Figure 2b. Piece of roofing shingle from soil with asphalt, glass fibers and colored granule.
    
 

Figure 3a.  Location of victim on ledge along stream
 

Bank Security Dye Packs/Dye Bomb Analysis
Contributed by Larry Peterson
 
Bank security dye packs or “dye bombs” have been utilized by banks for many years as a deterrent for bank robberies.  The dye packs are simulated stacks of currency which contain embedded electronics and chemical components which, when activated, emit a stream of red dye and tear gas designed to mark the currency, clothing and other objects in contact with the robber as well as to encourage the abandonment of the money.  The dye packs are activated electronically once the robber exists the bank.
The red dye is 1-methylaminoanthraquinone or MAAQ.  The tear gas is typically CS (orthochlorobenzalmalononitrile).  These two components can be considered characteristic of a security dye pack when found together.  The CS component however, may not be detectable depending on the history and nature of the item being tested.  The MAAQ component is not normally encountered in the environment and can be considered highly indicative of originating from a bank security device when found.  This dye is very difficult to remove from currency, clothing or plastic items such as car seats, motor cycle helmets or disposable gloves used to attempt the cleaning of stained money.  MAAQ has been used in the past in military smoke grenades and parachute smoke trails but is not a dye in current use for this.  MAAQ is used in the manufacture of red tail light lenses but will not be transferrable from the lens once the plastic is formed.
The identification of MAAQ begins with the visual identification of red stains.  The stains are extracted with an organic solvent such as chloroform, acetone or methanol.  The extracts are further characterized by the use of TLC, MSP, FTIR and GS-MS.  FTIR and GC-MS are considered confirmatory tests for the presence of MAAQ.  Tear gas components are also detectable by FTIR and GC-MS methods.
Major Referenced Cases:
No current listing of cases which have undergone a Daubert style hearing, however;  reference 1 discusses Daubert issues relevant to this issue.  Reference 2 lists a description of several actual cases where dye pack analysis was performed.


Additional References:

  1. Reynolds, P.C., “Analysis of Bank Dye Evidence and the Challenges of Daubert Hearings”, Forensic Science communications, Jan 2008, Vol. 10, No. 1

  2. Burds, K., and Djulamerovic, “Forensic Examination of Evidence Related to Bank Robberies Involving Bank Security Red Dye Pack Deployment”, Global Forensic Science Today, Issue 8, June 2009

  3. Egan, J.M., et al. “Bank Security Dye Packs: Synthesis, Isolation, and Characterization of Chlorinated Products of Bleached 1-(methylamino)anthraquinone”, J. Forensic Sci., November 2006, Vol. 51, No. 6

  4. Martz, R.M., Reutter, D.J., and Lassell, L.D., “A Comparison of Ionization Techniques for Gas Chromatography/Mass Spectroscopy Analysis of Dye and Lachrymator Residues from Exploding Bank Security Devices”, J. Forensic Sci., Jan 1983, Vol. 28, No. 1

 
Glitter Analysis  
Contributed by
 
Lamp Filament Analysis     
Contributed by Scott Ryland

In the course of vehicular accident investigations, the concern of whether the vehicle’s lights were illuminated or not often comes into question. The most obvious circumstance is apparent right of way violations when it is dark. Other situations also raise the controversy, such as head on collisions at night, turns without indicators, and motorcycle accidents, where the law requires continuous headlamp illumination on the motorcycle. In the case of rear-end collisions, it is sometimes argued that the vehicle hit did not have its brake lights or tail lights illuminated.

The request for examination is not only limited to motor vehicles. It can also arise in marine accident investigations involving boat lighting or buoy/channel lighting, or even in assault investigations where it is questioned whether the room’s lights were on or off.

With incandescent lighting, the question of whether the lamp was illuminated or not at the time of a forceful impact can often be answered by laboratory examination. The examination involves observation of lamp abnormalities, either by macroscopic examination or, more often, microscopic observation. Based on basic principles of physics (inertia) and chemistry (oxidation), the abnormalities observed indicate the condition of the lamp at the time of the impact that produced them. If there are no significant abnormalities observed, no direct conclusions can be reached.

Incandescent lamp filaments are typically constructed of coiled tungsten wire. As the wire heats due to resistance of the electrical energy passed through it, it emits light. The filaments are often coiled to increase the illumination intensity. Tungsten is rather rigid and brittle at ambient temperatures, but it becomes ductile at incandescent operating temperatures. Also, the metal will not oxidize at ambient temperatures, but readily oxidizes when exposed to the atmosphere at incandescent operating temperatures. The latter is why most traces of oxygen are evacuated from incandescent bulbs during their manufacture.

Hence, observation of the damage to a lamp filament produced by a forceful impact will often provide an indication of whether it was a.) hot and ductile versus cold, rigid, and brittle and b.) oxidized or not, if exposed to oxygen due to a fracture of the glass envelope. Deformation when hot results in uneven coil spacing, typically accompanied by arching of the filament coil. If the glass envelope is fractured, other indications of the filament’s temperature at the time of impact may also be present. A heavy tungsten oxide deposit forms on the surface of an incandescent filament, giving it a black appearance as opposed to the normal metallic luster. A different form of tungsten oxide is often deposited on cooler surfaces of the lamp, appearing as a white or yellow powder. If the lamp’s filaments were off when the glass envelope breaks, little of these oxides appear. Furthermore, an incandescent filament is extremely hot and minute fragments of the bulb’s broken glass will sometimes fuse and melt onto the filament’s surface. These deposits may be clearly seen with light or electron microscopic examination, and can even be chemically analyzed and characterized using a scanning electron microscope in conjunction with an energy dispersive X-ray spectrometer. If the filament was off, and cold, the glass fragments would simply bounce off the hard metal filament.

Sometimes, the inertia of the filament coil will be sufficient to cause a separation in the filament. Observation of the resulting abnormalities can also provide an indication if the lamp was on or off. If the lamp was on and the filament hot, it may be stretched and necked down to the point of separating. At that point a small high temperature electric arc occurs between the separated ends, sufficient to melt the tungsten metal. This leaves a small bulbous tip on the end of the necked-down filament. In the case of quartz-halogen headlamps, the filament assembly is much more rigid and the hot separation is typically not accompanied by a reduction in the wire’s diameter and has much larger bulbous tips. Conversely, if the lamp was off and the filament cold, it may fracture at a weak point in the wire. The resultant break has a very angular fracture surface, with no reduction in the diameter of the wire. The amount of force required to produce the latter is much greater than that for the former.

Normal lamp burn-outs produce a filament separation that somewhat resembles the hot separation in quartz-halogen headlamps described above. They, however, are not accompanied by filament distortion.

              

There are limitations to the analysis. First of all, the impact must have been of sufficient force to produce abnormalities beyond those typically observed in new and in-service lamps. Second, there is no analytical way of knowing when the impact producing the abnormalities occurred. Third, the duration that the lights were activated cannot be determined by lamp examination. Consequently, the lights may have been turned on a second before the impact in question. And finally, conflicting indications resulting from multiple impacts or tampering with the lighting circuitry following the accident may produce uninterpretable observations. Fortunately, the latter are typically recognizable based on observed lamp abnormalities.

The advent of non-incandescent vehicle lighting has reduced the demand for this analysis. The automotive market now also employs arc-style high intensity lamps and light emitting diode (LED) lighting fixtures, both devoid of tungsten filament light sources.

Additional References:

Baker, J.S., Fricke, L.B., Baker, K.S. and Aycock, T.L., Lamp Examination for On or Off in Traffic Collisions, 2003 edition, Northwestern University Center for Public Safety, Evanston, IL.

Severy, D.M., “Headlight-Taillight Analyses from Collision Research,” Proceedings of the 10th STAPP Car Crash Conference, Holloman Air Force Base, New Mexico, USA, Nov. 8-9,1966.

Dolan, D.N., Vehicle Lights and Their Use as Evidence,” J. For. Sci. Soc. (1971) 11:2.

Haas, M.A., Camp, M.J. and Dragen, R.F., “A Comparison Study of the Applicability of the Scanning Electron Microscope and the Light microscope in the Examination of Vehicle Light Filaments,” J. For. Sci. (1975) 20:91-102.

Powell, G.L.F., “Interpretation of Vehicle Globe Failures: The Unlit Condition,” J. For. Sci. (1977) 22:3:628-635.

Thorsen, K. A., “Examination of Bulb Filaments by the Scanning Electron Microscope,” Can. Soc. Forens. Sci. J. (1981) 14:2:55-69

Greenlay, W., Juzkow, M. , Mikkelsen, S., and Beveridge, A., “The effect of Impact on the Filaments of Quartz Halogen Headlamps,” Can. Soc. Forens. Sci. J. (1986) 19:2:77-82.

Steiner, J.C., Clark, N.E., and Thom, D.R., “Bulb Usage Analysis of LED-Type Automotive Lighting,” Technical Paper #2003-01-0892, SAE International, Warrendale, PA., USA (2003).

Ehmann, R. and Yu, J.C.C., “Determination of Energization State of Xenon High Intensity Discharge Automobile Headlights,” Forensic Science Journal (2009) 8:1:13-28.


 
Air Bag Analysis
Contributed by Glenn Schubert
 

In some incidents, law enforcement agencies have requested technical assistance from forensic scientists in determining the driver of a vehicle that was stolen and crashed, involved in a hit-and-run accident, or involved in a reckless homicide.  In the past, evidence such as hairs, fibers, blood and fingerprints found inside the vehicle were used to help make this determination.  Now, examination of the deployed airbags and the occupants clothing can provide some important evidence.

Most airbags use a solid-propellant type of inflator in the driver side and passenger side.  Side curtain airbags typically use stored gas for inflation. A sensor in the vehicle detects a sudden deceleration, not necessarily a collision, and sends an electrical current to the detonator in the inflator.  This causes a slow detonation of sodium azide or guanadine nitrate pellets in the inflator, resulting in the production of gas as hot as 7000C that inflates the airbag.  The airbag inflates in less than 1/20 of a second, at a speed of 200 miles per hour, with the hot gas.  The airbag begins to deflate immediately, as the hot gas escapes through vent holes in the back, making it a better cushion and absorbing the impact of the occupant.  The hot gas can also leak through small holes from the stitching seams in the front of the airbags.  If clothing from the occupants comes into contact with the airbag when it is at or near maximum inflation, the leaking hot gas can cause singe patterns on the front of the clothing, characteristic of the seam patterns.  The pattern typically appears as a series of small black dots or smears, 2-3mm apart.

In most automobiles, the driver side airbag is round with round seams, so it will produce arc-shaped singe patterns.  The vent holes may cause a singe pattern on the cuffs of the driver’s shirt if he is still holding on to the steering wheel when the airbag deploys.  The passenger side airbag is often rectangular in shape, with straight seams, so it will produce a straight singe pattern.  This makes it possible to differentiate the singe patterns produced by a driver side airbag from the one produced by a passenger side airbag.

The singeing occurs mainly on the clothing covering the chest and arms of a restrained front seat occupant.  Singeing can also occur on clothing covering the abdomen of an unrestrained front seat occupant.  The size and seam patterns can differ from one airbag to another, usually by make, model and year.  Because there are differences, you can have different class characteristics, thereby including or eliminating certain airbags as the source of a singe pattern.  Certain fibers, such as cotton and silk, singe more easily than man-man fibers, making the patterns easier to detect.  The singe patterns are difficult to observe on dark colored clothing. Wearing a seatbelt will likely reduce the opportunity for clothing to become singed.   De-powered and multistage airbags, now utilized in newer vehicles, will also reduce the chances of seeing a singe pattern on an occupant’s clothing.

Some driver side airbags might utilize corn starch or talc as a lubricant, depending on the sealant used on the interior surface.  Passenger side airbags do not have a sealant, so no lubricant material is used.  Of course, examinations for other types of trace material transfers, such as hairs and fibers, may also be probative and should also be conducted.

Additional References:

  1. Schubert, GD, Forensic Value of Pattern and Particle Transfer From Deployed Automotive Airbag Contact, Journal of Forensic Science, Nov 2005, Vol 5, No 6.

  2. Schubert, GD, Forensic Analysis On The Cutting Edge, Chapter 2, Forensic Analysis of Automotive Airbag Contact – Not Just A Bag of Hot Air; Wiley and Sons, 2007.


Fireworks Analysis  
Contributed by Micheal A. Trimpe

Fireworks analysis is much like the analysis of low explosives.  Pyrotechnic devices can be used in various crimes but are usually associated with nuisance and vandalism crimes. Pyrotechnic devices are, like other low explosives, constructed of an explosive powder confined in packaging with a wick for ignition (Fig. 1, 3) All of these components can be of interest to the trace analyst in identifying the device used in a crime.

As in most other trace evidence cases, the analyst searches debris under a stereomicroscope for microscopic pieces of evidence. The paper or plastic packaging can reveal identifying marks.  Quite often a small amount of unexploded powder will remain in the debris or paper wrapping.  Most often a burned, molten substance will remain in the exploded material and can be analyzed.  Occasionally the hands or clothing of a suspect can be examined for telltale microscopic pyrotechnic particles.

The analysis usually involves scanning electron microscopy with energy dispersive x-ray spectrometry (SEM/EDS) (Fig.2) for the inorganic make-up, while infrared spectrophotometry (FTIR) is used for the organic make-up of the chemical mixture.

Chemical and instrumental analyses can suggest the ingredients of the device.  Potassium perchlorate is still commonly used as an oxidizer in fireworks. Magnalium is popular for its white sparks and crackling effects.  Color effects are produced with different chemicals that include: strontium for reds, sodium glows yellow, magnesium burns extremely bright white, barium produces green, and a copper content can yield blues.

Fig. 1  Inside unburned firework device             Fig. 2 SEM micrograph

 Fig. 3 Assortment of pyrotechnic devices    

Additional References

  1. J. Conkling,  Chemistry of Pyrotechics, Marcel Dekkar Inc., 1985.

  2. D. Haarmann, The Wizard’s Pyrotechnic Formulary, 1990-1996.

  3. M.A. Trimpe, Analysis of Fireworks for Particles of the Type Found in Primer Residue (GSR),  Midwestern Association of Forensic Scientists Newsletter, Winter, 2003.

Lachrymators/Pepper Spray Analysis
Contributed by
 

Feather Analysis

Contributed by Marcy Heacker and Carla J. Dove, PhD

Feather analysis can be utilized to identify the avian group or bird species in a variety of investigations and circumstances. Historically, morphological feather identification techniques were developed and utilized at the Smithsonian Institution, National Museum of Natural History for the determination of bird species involved in bird/aircraft collisions (“bird strikes”). In addition, feather identification techniques have been successfully used in the identification of bird species in feathered anthropological artifacts, prey remains, food contaminants and law enforcement cases.

While molecular analysis of bird remains and feather material has become an important part of the identification process – the traditional morphological analyses are still vital to the identification process. Depending on the material available, morphological feather analysis can be approached two different ways – whole/intact feather examination (feathers or feather fragments with color/pattern) and microscopic feather examination.

For most cases with intact/whole feathers or significant feather material, the evidence can be directly compared to a vouchered bird specimen (usually in a museum or university collection). Whole feather characters, such as feather size, color and pattern, are found in the pennaceous feather region – the distal part of a feather typically seen on a bird. These macro-characters can frequently be matched to known bird feather reference. It is important to consider where on the bird and what part of the feather the unknown material is from. Photographic comparisons of the unknown sample with vouchered bird specimens are helpful in case documentation. Also, consulting an ornithologist to assist in interpreting feather material and possible species plumage variation is important in all feather identification cases. Many times, identifications using whole feather material can be made to species level; however, matches with an individual bird may not be possible.

Microscopic feather analysis of the plumulaceous (downy) region of a feather can be diagnostic to the “group” (usually taxonomic order) of bird. Despite this limit, microscopic feather examination can be very helpful in the identification process. Microscopic feather characters can help focus and corroborate examination of whole feather material – and many times is the only technique available for minute or fragmented feather material. Standard comparison light microscopy (100-400x magnification) is the best way to examine plumulaceous feather material by comparing the unknown to referenced vouchered microslides. Scanning electron microscopy (SEM) can be used for analysis, but internal pigment patterns are an important micro-character that SEM cannot provide.

As with many trace evidence materials, the examiner needs to understand the variation that is possible with feathers – particularly in the microscopic plumulaceous feather characters. These characters are transitional in nature. Generally, character expression gradually changes along the feather barbules and barbs, along an individual feather and on the location of the bird’s body.

While feather evidence is uncommon, the application of macro and micro feather analysis can be useful in interpreting avian material and is a tool for the forensic examiner.

Additional References – Feather Analysis

Deedrick, D.W, and J.P. Mullery. 1981. Feathers are not lightweight evidence. FBI Law Enforcement Bulletin 50(9):22-23.

Dove, C.J. and Koch, S.L. 2010. Microscopy of feathers: A practical guide for forensic feather identification. JASTEE 1(1):15-61.

Robertson, J., C. Harkin and G. Govan. 1984. The identification of bird feathers: Scheme for feather examination. Journal of Forensic Science Society 24(2):85-98.

Scott, S.D. and C. McFarland. 2010. Bird Feathers: A Guide to North American Species. Stackpole books.

Slater Museum of Natural History. 2005. Wing and Tail Image Collection. The University of Puget Sound. 20 May 2015. .

U.S. Fish and Wildlife Service Forensics Laboratory. 2010. The Feather Atlas: Flight Feathers of North American Birds. 20 May 2015.
 
Cordage Analysis
Contributed by Karen Lowe

A cordage examination begins after all other trace evidence has been collected and the remainder of forensic examinations have been conducted on the cordage.  First, an overall assessment of the color and construction (e.g. twisted, braided) of the cordage is conducted, and characteristics such as crowns per inch, number of plies, direction of twist (“S” or “Z”) and diameter are examined .

Pieces of cordage are then examined to determine if ends of cordage from different locations/people can by physically fit together.  This may be possible with plastic-like cordage or cordage with a paper or fabric core or tracer. If the cordage has a paper or fabric core or tracer, the core is opened to examine the edges/contours of the paper or fabric.  If the edges/contours of the paper or fabric physically fit together, it can be concluded that they were once one piece of cordage.

If a physical fit is not possible, the color, construction and composition of the cordage are examined and compared.  The examination of the color involves the macroscopic color of the items being compared as well as the microscopic color of the fibers comprising the cordage, which is examined as part of the fiber examination.  If the macroscopic color and the construction is the same, a textile fiber examination is conducted on the fibers comprising the piece(s) of cordage to determine composition.

If the color, construction and composition are consistent between pieces of cordage being examined, it can be concluded that they are consistent with originating from the same source, or another source with the same color, construction and composition.

Additional References:

1.      ASTM Standard E2225-10, “Standard Guide for Forensic Examination of Fabrics and Cordage,” ASTM International, West Conshohocken, PA, 2010, www.astm.org.

2.      Wiggins, K., Recognition, Identification and Comparison of Rope and Twine, Science and Justice, 1995, 35(1), pp. 53-58.


Wood Analysis    
Contributed by Michael A. Trimpe

A piece of wood as large as a chunk of a tree left on the bumper of a car in a hit and run, or as small as a fragment on the tip of a bullet, can be identified by microscopy.  The quality of the sample in question dictates the potential degree of identification.  For example, a minute piece of sawdust may only be identified as a softwood versus a hardwood.  Some wood samples may be identified to their genus or family, for example Pinus (pine).  Still others may be identified to their species like Pinus resinosa (red pine) or Quercus alba (white oak).

The size of the piece of wood in question greatly determines how the sample should be prepared for microscopic identification.  If the sample is large enough, the analyst will observe the color and odor.  Then its gross features will be observed under the stereomicroscope.  This initial observation will include looking at the cross section to determine if it is a hardwood (with vessels) or a softwood (without vessels) (Fig. 5).

Then the sample is prepared for more detailed observation under higher magnification with a comparison microscope.  Microscopic thin sections of the wood are viewed from three cut angles.  A cross section (Fig. 1) cuts across the diameter of a tree, as would be made to cut the tree down. A radial section (Fig. 2) is cut perpendicular to the cross section and along the rays that run from the center of the tree to its outer edge.  A tangential section (Fig. 3) is cut perpendicular to the cross section and perpendicular to the radial section.  The cuts are typically made by hand with a sharp blade, but if the sample is already microscopic then a histological microtome could alternatively be used to cut the sample.  A red dye (Safranin-O) is often used to stain the wood sample for easier identification under the microscope.

After the wood sample is prepared and mounted on a microscope slide, the three thin sections are observed for identifying characteristics using a wood identification key.  Many keys are available in literature which are followed step by step until a species identification can be made.

Quite often wood identification is used in fire debris cases in which it is necessary to know if the wood collected at the scene is a softwood. Softwoods are known to naturally emit terpenes (found in turpentine) which may cause complications with examinations for ignitable liquids.  Even charred wood can be identified using these methods(Fig. 4).  Wood identification can also be important in assault cases where splinters left in the victim can be compared to a wooden object used as a possible weapon.

   

Fig 1. Yellow Pine Cross-section                   Fig 2. White Pine Radial Cut                           Fig 3. Tangential Cut

 

Fig 4. Charred Yellow Pine                             Fig 5. Hardwood vs Softwood Cross-section

Additional References:

  1. R. Bruce Hoadley, Identifying Wood Accurate Results with Simple Tools, Taunton Press, 1990.
  2. H.A. Core, W.A. Cote, and A.C. Day, Wood Structure and Identification, Syracuse University Press, 1979.
  3. R. Summitt, A. Sliker, CRC Handbook of Materials Science, Vol IV, Wood, CRC Press, 1980.
  4. H.L. Edlin, What Wood is That?, The Viking Press, New York, 1984.
  5. W.A. Cote, Papermaking Fibers, Syracuse University Press, 1980.
  6. Panshin A.J., Zeeuw C., Textbook of Wood Technology, McGraw-Hill Book Co. 1970.
     

Match Analysis   
Contributed by
 
Cosmetics Analysis   
Contributed by
 

Cigarette Butt Identification Analysis 
Contributed by Michelle B. Clarke, Ph.D.

The butts of smoked cigarettes may be encountered at crime scenes.  Identifying the brand may help identify the smoker.  In addition, some brands of cigarettes have manufacturing numbers on them.  These numbers may also be present on packs or cartons which could provide further associative evidence.  Manufacturers are often willing to provide the significance of these numbers to assist in investigations.

A cigarette butt identification aid was published by Bob Bourhill, with the Oregon State Forestry Department.  Unfortunately, the last edition was published in 1992, and the information about specific brands is thus out of date.  The methods used in identifying cigarette butts, however, are still valid.  In the guide, cigarettes were given a numeric code based on physical attributes such as: presence/type of filter, coloration, diameter, presence/types of ventilation holes, colored bands, and printing/writing on the butt.  A suspect butt would be coded and compared to other cigarettes that matched the code.  There are several factors not considered in the guide that may be helpful in identifying cigarette butts today. Fire Standards Compliant (FSC) cigarettes are required in the United States.  FSC cigarettes use bands on the cigarette paper.  The bands are composed of materials that are intended to slow the burn rate of the cigarette.  The width and spacing of the bands, if present, may help identify a cigarette. Another characteristic of cigarettes which may aid in identification is plug wrap.  In addition to tipping paper, filtered cigarettes may use plug wrap to contain the filter and help maintain its size.  The use of plug wrap as well as the adhesive used to secure it may help distinguish a butt.   Finally, if the butt contains unburnt tobacco, the tobacco may be analyzed for flavoring constituents such as menthol.

Bourhill’s cigarette guide included only cigarettes.  Today, little cigars are becoming increasingly popular.  The design of little cigars often mimics that of cigarettes with the cigarette paper being replaced by a material containing tobacco, such as reconstituted sheet tobacco.  Thus, a cigarette butt which appears to have dark brown paper may be a little cigar, and little cigars must be considered in an identification scheme.

Utilizing the above techniques may identify a brand or indicate possible brand(s).  A scan of the internet will easily identify well over 1000 varieties of cigarettes and little cigars that can be purchased in the United States alone.  Maintaining a current library of every available product and its attributes is not realistic given the resources available in forensic laboratories.  The identification of a brand is largely reliant on the expertise of the examiner, and communication with manufacturers is often essential in the final determination.


Additional References:

  1. Cigarette Butt Identification Aid, Bob Bourhill, Oregon State Department of Forestry, 1992.

  2. The Design of Cigarettes, Colin L. Browne, Hoechst Celanese, 1990.

Entomological Analysis 
Contributed by Aaron Tarone

Department of Entomology, Texas A&M Uiversity

Forensic Entomology, broadly speaking, is the study of the use of insect and arthropod biology in the legal system. Insect evidence can be encountered in civil and criminal law. Civil evidence is typically related to disputes over causes of infestations of food, products, structures, and people. Insects are typically encountered in the criminal legal system to address issues related to neglect, abuse, and to provide information related to the timing, location, or toxicology of a death.

Frequently forensic entomologists are expected to provide information regarding the timing of a death as some taxa colonize remains soon after death and develop in a fairly predictable manner. This application has resulted in the perception that forensic entomologists provide a postmortem interval or minimum postmortem interval estimate. However, there are a number of assumptions that are associated with connecting estimates of insect age to the postmortem interval, which means that unless all violations of these assumptions can be ruled out such an assumption may be invalid. As an example, some insects can colonize vertebrates before death and in this case an estimate of insect age will not align with the postmortem interval. It is more appropriate to think of the postmortem interval or minimum postmortem interval as the null model for what insect evidence can provide to a legal investigation, which is only true if such assumptions are not violated.

In all instances of forensic entomology, the proper identification of the species in evidence is critical to developing opinions from the evidence. In many cases, there are taxa that can be easily mistaken for each other. Accordingly, it is important to use proper molecular methods and/or an expert on the type of insect in evidence to come to derive the best conclusions from that evidence.

Expert witnesses can be found through the American Board of Forensic Entomologists (http://www.forensicentomologist.org/).

The following reading can provide further details:

Byrd and Castner 2009, Forensic Entomology: The Utility of Arthropods in Legal Investigations

Amendt and Villet 2011, Advances in Entomological Methods for Death Time Estimation, Forensic Pathology Reviews

Tomberlin et al. 2011, A Roadmap fo Bridging Basic and Applied Research in Forensic Entomology, Annual Review of Entomology

Amendt et al. 2011, Forensic Entomology: Applications and Limitations, Forensic Science Medicine and Pathology

Gennard 2012, Forensic Entomology: An Introduction

Rivers and Dahlem 2014, The Science of Forensic Entomology
 
Palynology
Contributed by Vaughn M. Bryant

Palynology (the study of pollen and spores) has historically been underutilized as trace evidence in forensic science.  The focus of “forensic palynology” is on evidence obtained from the study of pollen and spores that is associated with a crime scene or is considered evidence related to situations involving the law.  As a discipline, the first recorded use was a little more than one-half century ago, but even today the use of this technique is relatively unknown or under-utilized in many regions of the world.

The analysis of pollen and spores (collectively called palynology) is recognized as an effective forensic tool for a number of reasons.  First, many types of pollen producing plants (angiosperms and gymnosperms) and spore-producing cryptograms (algae, fungi, ferns, mosses, liverworts, etc.) disperse vast quantities of pollen or spores as part of their reproductive process and rely mostly upon wind currents to carry these single-celled pollen or spores from the dispersal source to another location where they can carry out part of the reproductive cycle.  The inefficiency of this process results in the majority of these dispersed cells falling to the ground and forming a record of the vegetation in the immediate area.  Even though there is not a one-to-one correlation between the percentages of each pollen or spore type with the actual percentages of plants in the local vegetation, the record for each location becomes an effective way to identify various regions in the world.  A second important aspect as to why pollen and spores are effective forensic clues relates to their microscopic size that enables them to become trapped or deposited on almost any type of surface.  That aspect enables them to become effective clues that can often link a suspect, or some object, with a precise geographical region or a specific crime scene. A third factor that makes forensic palynology useful is that each plant species produces a unique type of pollen or spore, which can often be identified to the genus or species level using various types of microscopy including: light microscopy (LM), scanning electron microscope (SEM) and/or the resolution precision of transmission electron microscopy (TEM).  Because crime scenes and other geographical locations often contain a unique blend of plants, the pollen and spore evidence from suspects or items can often link them with precise locations. The fourth reason that palynology becomes a useful type of forensic evidence is that the majority of pollen and spores are highly resistant to destruction or decay.  That ability enables critical evidence, if collected and stored properly, to be examined and validated for years, decades, or even longer after a crime or event has occurred.

There are two different fields of forensic palynology, based upon the types of information or investigations that each pursues.  Although some forensic palynologists work in both areas, each group tends to specialize and focus mostly on one type of investigation.  The primary type of forensic palynologist works directly with the investigation of crimes as they pertain to situations involving victims, suspects, actual crime scenes, or associated items.  They usually work directly with local, state, or national law enforcement agents as part of those agencies or as personnel in forensic agencies. The second type of forensic palynologist works mostly with questions related to finding the original locations of objects.  That type of individual often examines items of unknown origin and is asked to use the pollen and spore evidence associated with the item to determine the item’s geographical origin.

During the past decade the world has become a more dangerous place to live.  The availability of rapid travel and instant communication across continents, coupled with the worldwide rise in terrorism and local/regional conflicts have created many unsafe regions. Although there is no simple solution to all of these problems, the wider use of forensic palynology as trace evidence might help identify and prevent the wider spread of criminal activity and international terrorism.

Additional References:

  1. Milne, L.A., Bryant, V.M., and Mildenhall, D.C., Forensic palynology.  In:  Forensic botany: principles and applications to criminal casework (ed. H. Coyle), CRC Press LLC, Boca Raton, FL, pp. 217–252. (2005).

  2. Bryant, V.M., and Jones, G.D. 2006.  Forensic palynology: current status of a rarely used technique in the United States of America.  Forensic Science International 163: 183–197.

 Footwear and Tire Impression Examinations  
Contributed by Cheryl Lozen

A footwear or tire track impression left at a crime scene can be utilized by an investigator in an effort to establish if there is a connection between the impression and some suspected known footwear or tire.  Other aspects of the crime may also possibly be determined such as the number of persons or vehicles involved, mode of entry, direction of travel, make and model of footwear or tire, etc.  

Impressions can be three-dimensional when left in snow or soft soil, or they can be two-dimensional when a dirty, bloody, or wet origin impression is left on a surface. Questioned impressions from crime scenes can be photographed, lifted, or cast with a variety of materials to preserve for further examination.  Many methods of enhancement can be performed to help visualize and collect the scene impressions as well.

Footwear and tire impressions are examined in a similar fashion to each other. Examinations are performed utilizing various visualization and enhancement methods including lighting techniques, photography, magnification, chemical enhancement, powdering,  lifting, and processing with computer software.

The primary task of a footwear/tire track examiner is to determine whether or not a particular footwear or tire could have made the scene impression.   If there is sufficient detail to do so, a comparison of physical size, tread designs and/or general wear patterns can lead to an elimination or an association. The questioned impression and known footwear or tire must correspond in the class characteristics of design, physical size, and general wear (if observed) in order to be associated.  

The highest degree of association expressed by a footwear and tire impression examiner is an identification. This requires that the questioned impression and the known footwear or tire share agreement of class characteristics along with randomly acquired characteristics (such as scratches, cuts and stone-holds) of sufficient quality and quantity.  It will be the opinion of the examiner that the particular known footwear or tire was the source of, and made the questioned impression.

If there is agreement of class characteristics but insufficient detail to compare randomly acquired characteristics (or they are absent) the resulting opinion of the examiner will be that the known footwear or tire is a possible source of the questioned impression and therefore could have produced the impression. Other footwear or tires with the same class characteristics observed in the impression would also be included in the population of possible sources.

If there are unexplainable differences in class characteristics and/or randomly acquired characteristics, the resulting opinion of the examiner will be that the known footwear or tire did not produce the questioned impression.

An unknown footwear or tire impression can also be searched in a laboratory or commercially available database to determine the possible make and model of shoe or tire that could have made that impression.  There are no databases available at this time however, that contain all makes and models of footwear and tires.

Calculations of tire track width, turning diameter and wheel base measurements at the crime scene can be utilized to generate a list of possible makes and models of vehicles that have similar measurements to the crime scene tire track impressions.

Comparison of barefoot morphological and sock-clad foot impressions from known standards to crime scene impressions is also performed by some examiners. This may also include comparison of barefoot morphological impressions on a shoe insole to known standards in order to identify the possible owner of a shoe from discarded or lost footwear.  Barefoot morphology refers to the shape of the foot, and does not include the examination of friction ridge skin impressions.

References

www.swgtread.org

www.theiai.org

Abbott, J. R., Footwear Evidence, Charles C. Thomas Publisher: Springfield, IL, 1964.

Bodziak, W. J., Footwear Impression Evidence, 2nd ed., CRC Press: Boca Raton, FL, 2000.

Bodziak, W. J., Tire Tread and Tire Track Evidence, CRC Press: Boca Raton, FL, 2008.

Cassidy, Michael J., Footwear Identification, Canadian Government Publishing Center, 1980.

Footwear and Tire Impression Crime Scene Recovery

Contributed by Lesley Hammer

The purpose of footwear and tire track impression crime scene recovery is to document the location and orientation of these impressions and to provide an accurate representation of the features of the impression for examination by a forensic physical impression expert.

When a person or a vehicle travels to and/or within a crime scene, impressions of footwear and/or tires are left. Footwear and tire impressions are typically classified as 2- or 3-dimensional.  2-dimensional impressions are made when a substance is deposited on or removed from a surface by a footwear outsole or tire tread.  3-dimensional impressions are made when the sole or tread is impressed into a substance such as snow or mud.  Documentation and collection of footwear or tire impression evidence is accomplished through the use of photography and other processing techniques such as lifting, casting and chemical development.

Photography

A high quality photograph and specialized lighting techniques are utilized to capture sufficient detail.  A variety of photographs are taken to document the impressions within the scene as well as close ups for enlargement and examination.  Close up photographs for examination should include a scale, with the camera positioned directly above and parallel to the impression.  Photographs are taken of impressions before other techniques for collection are applied.  Tire impressions, due to their length, are photographed in overlapping sections, later the individual photographs may be pieced together to represent the length of the tire track.

Casting

3-dimensional impressions are cast with a material that will retain the features and physical size of the impression accurately.  Dental stones (gypsum cement) is commonly used for this purpose.  It is mixed with water in the proper ratio and carefully poured into the impression.  After it hardens, it is labeled and collected.  Coatings such as paint or hairspray are used in some impression conditions to improve the cast.

Lifting

2-dimensional impressions may occur in dust.  Electrostatic lifters may be used to transfer dust impressions to a sheet of metallic backed black material for contrast and preservation. They also may be left in a variety of materials that were moist and then dried, such as water or mud.  2-dimensional impressions of many types may be lifted using gelatin lifts (gelatin material on rubber backing) or through the use of sheets of adhesive material.

Enhancement

Impressions may be enhanced using a wide variety of techniques, depending upon the substance that constitutes the impression.  Oil or dried moisture impressions may be enhanced using powder brushed onto the impression.  Impressions in blood are enhanced with reagents that stain or react with components of blood.  Reagents that react with other substances such as minerals (iron, calcium carbonate) or proteins (amino acids) may also be used to enhance impressions, usually when the original impression is able to be transferred to the laboratory for processing, such as a dust impression on a piece of paper.  Specialized forensic photography utilizing lighting and filters may also be used to enhance impressions.

These documentation and collection techniques may be applied to preserve and record other types of impression evidence, such as impressions of bare feet, gloves or other types of tracks.

This document is intended to provide general information about the collection and processing of footwear and tire impression evidence and is not intended to be a guide or to be inclusive of all possible procedures and methods for the collection of impression evidence.

References

www.swgtread.org

www.theiai.org

Bodziak, W. J., Footwear Impression Evidence, 2nd ed., CRC Press: Boca Raton, FL, 2000.

Bodziak, W. J., Tire Tread and Tire Track Evidence, CRC Press: Boca Raton, FL, 2008.

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