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:
1. Budworth G. Knots and Crime. Great Britain: Police Review Publishing Co. Ltd., 1985.
2. Chisnall R. The Forensic Analysis of Knots and Ligatures. Salem, Oregon: Lightning Powder Company, Inc, 2000.
3. 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.
4. 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.
5. Chisnall R. Knot-tying habits, tier handedness and experience. The Journal of Forensic Sciences, 2010, Volume 55, No. 5, pp. 1232-44.
6. 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
7. 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
8. Nute, H.D. Mirror images in knots. Journal of Forensic Sciences 1986, Volume 31, No.1, pp. 272-9.