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Forensic hair analysis is a scientific method of analyzing trace evidence from a crime scene. The process involves examining the hair shaft including the medulla (inner) layer, the cortex (intermediate layer) and the cuticle (outer layer). The analysis is done using powerful microscopes to find NDA evidence in the tissue left on the hair shaft. Evidence from the hair is collected and analyzed under a special protocol. Forensic hair analysts undergo specific training and use special technology to ensure that their work holds up in court (Bisbing, 1982). This concept was first mentioned by a French scientist Edmund Locard who discovered that people can easily transfer and pick up trace materials such as fibers, hair and dust without knowing. He then realized that this exchange can be a key to analyzing a crime scene. This formed the basis for his “Locard Exchange Principle” which became the foundation of forensic science in the early 1900s. Later, Paul L. Kirk of the United States came up with the fundamentals of microscopic hair analysis which are today used by scientists (Mayr, 1982).
Importance of forensic hair analysis
Forensic hair analysis is done by investigators to assist them in identifying individuals who were involved in a crime. The forensic hair analysts start by determining whether the hair came from the victim, the suspect, or it was an animal hair. If the hair matches that of the victim, it is then used to identify the victim. However, if it does not match that of the victim, it may belong to the criminal. In that case, it is used in obtaining information about the relationship between the crime perpetrator and the crime scene and also between the perpetrator and the victim. It may also be used to exonerate other suspects since it assists in the elimination of suspects (Barnett & Ogle, 1982).
Forensic hair comparisons
The process of forensic hair comparison is basically grounded on the scientific principles of microscopy, biology, anatomy, histology and anthropology. It involves assessing the phenotypic characteristics of human hair by observing the microscopic anatomy of that hair to determine the body areas and racial characteristics of that hair.
Therefore, before the forensic hair comparison is done, the race and body area must be identified. At this stage, hair is classified into three racial groups namely Caucasian, Negroid and Mongoloid. Caucasian is the hair of European origin; Negroid is hair from Sub-Saharan Africa while Mongoloid means hair of Asian or Native American descent. Hairs, which fail to be associated with these three classes, are said to be exhibiting mixed traits or not to belong to any of the three classes. However, this hair may still be useful for microscopic comparison purposes. The other classification of human hair is based on the part of the body that it came from. This is done in addition to the three racial groups’ classification and is done with considerable accuracy. According to the body area, human hair can be classified as head hairs, which are from the scalp, pubic hairs, facial hair, which is from the beards and mustache, limb hairs, which are from the arms or legs, chest hairs, axillary hairs from the armpit, and eyebrow/eyelash hairs. Other hairs may be encountered which are not from any of these areas and are referred to as transitional hairs such as the hairs found between two body regions (Oien, 2009).
Procedure for forensic hair comparison
Once the ethnic origin and the body area have been determined, this is followed by determination of the suitability of that hair for comparison. Hairs, which have been identified as head hair or pubic hairs, are normally accepted for comparison with a sample that is known to be from the head or the public. Hairs form the other parts of the body are considered not suitable since they generally lack the needed distinction in their microscopic characteristics, which can be reliable in distinguishing hairs from different persons. Their comparison with a sample can only be done in restricted circumstances and with restricted significance (Houck et al., 2004).
Once the suitability for microscopic comparison has been determined, the hair is then compared with the appropriate known sample. This means that hairs from the head are to be compared with sample from head hairs and this also applies for the pubic hairs. The process of hair comparison involves analyzing the questioned hair and its known sample side-by-side with a comparison microscope. This provides a possibility of prompt comparison of the microscopic features of the hair in question with the same areas of the known sample at the same time and in a similar field of view. This must be done on the entire hair and along its entire length.
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According to guidelines by the Scientific Working Group for Materials Analysis (SWGMAT) (2005), for the analyst to conclude that the hair in question and its known sample are consistent in their characteristics and share a common origin, it must be determined that there is no significant difference between the two. This means that the characteristics seen in the hair must be represented in the known sample. The initial point in forensic hair examination is an attempt to find the differences and not similarities between the hair in question and its known sample. This is because hairs being biological products, they are subject to genotypic and phenotypic influences on their microscopic characteristics arrangements. Therefore, no two hairs can look exactly alike even if they are from the same individual. Therefore, during the analysis, it should not be expected that the hair in question and its known sample will exhibit identical features along the entire hair length (SWGMAT, 2005).
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After the analysis, there are three general conclusions that can be made; exclusion, no conclusion or association. Exclusion means that the hair does not come from the owner of the sample. “No conclusion” is made when the hair in question exhibits similarities with its known sample, but shows some slight differences during the microscopic analysis. These differences may, however, not be adequate to make a conclusion that the hair does not originate from the owner of the sample. Some of the slight differences may be due to a lot of time elapsing between the deposition of the hair and the collection of its known sample or significant differences in the length of the hair and its sample.
Analysis may, on the other hand, conclude that there is an association when the hair in question exhibits similar microscopic characteristics as that of the known sample. In such a situation, the analysts may conclude that the hair came from the donor of the sample. This is when all the microscopic characteristics in the hair in question are presented in the known sample (Hicks, 1977).
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Studies on forensic hair comparison
Various studies have been carried which support microscopic examination of hair for comparison. Strauss (1983) made an experiment that involved 100 people 54 of them being Caucasian, 27 Mongoloid and 19 Negroid. 7 head hairs were obtained from each of 100 individuals to ensure that there was a wide variation. The hairs were placed on a glass microscope slides and were defined as the known samples. In addition, one hair was obtained from the 100 people to be used as the hair in question and also mounted on the glass microscope slides. All the hairs (700 known samples and 100 hairs in question) were characterized individually, and a set of seven experiments carried out. A neutral person then selected 10 hairs in question for comparison with their 10 known samples. Microscopic comparison exhibited 100 percent accuracy in correlating the hair in question with their known source and the samples. The study also demonstrated that the hairs were correctly identified according to the races of the persons (Strauss, 1983).
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Another study was conducted by Gaudetter and Keeping (1974) who collected head hair samples from 100 people. Among them, 92 were Caucasian, 2 were Negroid and 6 were Mongoloid hairs. From the 100 samples, 6 to 11 microscopically different hairs were selected to represent various microscopic characteristics which were present in the known sample. The hairs were microscopically characterized and categorized using punch cards according to their specific microscopic characteristics. The cards from each individual were mixed with those of others and then sorted based on similar holes on the punch card. Te hairs on each of the similar cards were then compared microscopically, and a total of 861 were examined and compared for 370,230 times. From all these comparisons, only 9 hairs could not be distinguished (Gaudette & Keeping, 1974).
In another study, Gaudette (1976) obtained 30 pubic hairs from 60 people who were all Caucasians. From these hairs, 6 to 11 different hairs were randomly selected to represent the various characteristics in the 30 hairs. The characteristics being set on punch cards just as in the previous experiment and the cards mixed and sorted. A total of 454 hairs were compared in 102, 831 times. Only 16 pairs of hairs could not be distinguished (Gaudette, 1976).
Forensic hair analysis has been found to be an effective method of identifying criminals. The studies conducted have also proved that the method can be effective. However, for it to be successful, it requires specifically trained analysts.