Scientific working group on materials analysis position on hair evidence.

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 a direct association between the crime and the criminal, which, of course, should be the goal of any forensic investigation. The first step in any hair examination is to separate the hairs from the submitted evidence. Some cases may result in the collection of relatively few hairs, while other cases may result in the recovery of hundreds or even thousands of hairs when numerous items or items such as vacuum sweepings or bedding are submitted. When hairs are first isolated from an item of evidence, a microscopical examination can initially determine which hairs may have evidential value out of the myriad of hairs that are often recovered. An example of hairs having potential evidential value would be those found on the victim's clothing or in their environment that are microscopically dissimilar to their own hairs. Hairs deemed to have potential evidential value will then be considered for further detailed microscopical comparison and possible DNA analysis. This initial screening step must be done by examining the hairs that are collected during the investigation of a crime using a good quality microscope capable of high magnification and conducting a brief yet detailed microscopical comparison. A detailed microscopical examination is necessary to isolate these hairs because it is common for hairs from different individuals to look the same macroscopically but differ microscopically. Unfortunately, many laboratories have adopted screening methods which rely solely on low level evaluations of hairs with a stereomicroscope to isolate those for DNA analysis that are macroscopically dissimilar in color and shape from the submitted known hairs. Screening methods used by other laboratories are even less discriminating in that they simply choose all hairs with root tissue and run nuclear DNA analysis on them regardless of their appearance. Ultimately, any procedure which does not include a detailed microscopical examination will likely result in hairs of probative value being overlooked or in time and money being wasted conducting DNA analysis on nonprobative hairs. Once hairs of interest are isolated, the microscopical analysis of these hairs can provide investigative information such as the racial characteristics of the hair donor, the somatic origin of the hair, the growth phase of …