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.
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2. Scientific working group on materials analysis. Human hair examination guidelines. Forensic science communications 2005; 7(2).
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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)
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.
2. 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.
3. 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.
4. 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.
5. State of New York vs. Anne Trovato, 2006 - Patricia Mery
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.