ated” through microscopic examinations, 9 of them (12.5 percent) were found in fact to come from different sources when reexamined through mtDNA analysis.87 This illustrates not only the imprecision of microscopic hair analyses, but also the problem with using imprecise reporting terminology such as “associated with,” which is not clearly defined and which can be misunderstood to imply individualization.

In some recent cases, courts have explicitly stated that microscopic hair analysis is a technique generally accepted in the scientific community.88 But courts also have recognized that testimony linking microscopic hair analysis with particular defendants is highly unreliable.89 In cases where there seems to be a morphological match (based on microscopic examination), it must be confirmed using mtDNA analysis; microscopic studies alone are of limited probative value. The committee found no scientific support for the use of hair comparisons for individualization in the absence of nuclear DNA. Microscopy and mtDNA analysis can be used in tandem and may add to one another’s value for classifying a common source, but no studies have been performed specifically to quantify the reliability of their joint use.


Fibers associated with a crime—including synthetic fibers such as nylon, polyester and acrylic as well as botanical fibers such as ramie or jute, which are common in ropes or twines—can be examined microscopically in the same way as hairs, and with the same limitations. However, fibers also can be analyzed using the tools of analytical chemistry, which provide a more solid scientific footing than that underlying morphological examination. In some cases, clothing and carpets have been subjected to relatively distinctive environmental conditions (e.g., sunlight exposure or laundering agents) that impart characteristics that can distinguish particular items from others from the same manufacturing lot. Fiber examiners agree, however, that none of these characteristics is suitable for individualizing fibers (associating a fiber from a crime scene with one, and only one, source) and that fiber evidence can be used only to associate a given fiber with a class of fibers.90


Houck and Budowle, op. cit.


E.g., State v. West, 877 A.2d 787 (Conn. 2005); Bookins v. State, 922 A.2d 389 (Del. Supr, 2007).


See P.C. Giannelli and E. West. 2001. Hair comparison evidence. Criminal Law Bulletin 37:514.


See, e.g., R.R. Bresee. 1987. Evaluation of textile fiber evidence: A review. Journal of Forensic Sciences 32(2):510-521. See also SWGMAT. 1999. Introduction to forensic fiber examination. Forensic Science Communications 1(1). Available at, which includes the following summarization in Section 5.4: “It can never be stated with certainty that a fiber originated from a particular textile because

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