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Friday, April 14, 2017

Forensic Hair and Fiber Identification: An Inexact Science

     Forensic analysts who microscopically compare crime scene hair follicles with samples from a suspect's head or other part of the body note similarieties or differences in hair length, thickness, texture, curl, color, and appearance of the medulla, the stip of cells that runs up the center of the hair shaft. A follicle, however, cannot be individualized like a fingrprint. A hair identification expert can declare, for example, that the defendant's hair looks like a crime scene follicle, or is consistent in appearance with the questioned evidence, but they are not supposed to testify that a follicle at the scene of a crime could have come from the defendant and no one else. What nobody knows about forensic hair identification is this: if two follicles look alike in all respects, what are the chances they have come from the same person? Just how strong an identification is this, and how incriminating?

     Hair identification experts also analyze crime scene strands of fiber and compare them with samples of clothing, carpets, blankets, and other fabrics associated with the defendant. Fibers can be distinguished by material, shape and color--there are 7,000 dyes used in the United States. A fiber expert can testify, for example, that a fiber on a murder victim's body is consistent in appearance with carpet fibers from the trunk of the defendant's vehicle. To go further than that is crossing the line, scientifically.

     Up until the mid-1990s, hair and fiber experts were routinely pushing the scientific envelope by identifying crime scene follicles and fibers the way an expert would identify a latent fingerprint. In hundreds, if not thousands of cases, defendants went to prison on the strength of this form of expert testimony. When DNA came on the scene, abuses in hair and fiber identification were exposed, and the scientific unreliability of these matches was dramatically revealed.

     In Texas alone, between 1995 and 2002, DNA analysis exonerated 30 men who had been convicted solely on crime scene hair identification. Dr. Edward Blake, the Berkeley, California DNA pioneer, put forensic hair identification in perspective: "They did it because they could get away with it. A defendant in Idaho and another in Florida were sent to death row in cases where the only evidence against them were jailhouse informants and crime scene hair identifications."

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