Here’s Giannelli on hair and fiber analysis:
In 1995, a federal district court in Williamson v. Reynolds observed: “Although the hair expert may have followed procedures accepted in the community of hair experts, the human hair comparison results in this case were, nonetheless, scientifically unreliable.”77 The court also noted that the “expert did not explain which of the ‘approximately’ 25 characteristics were consistent, any standards for determining whether the samples were consistent, how many persons could be expected to share this same combination of characteristics, or how he arrived at his conclusions.”
Williamson, who was five days from execution when he obtained habeas relief, was subsequently exonerated by DNA testing. 79 The Williamson opinion — perhaps the only thorough judicial analysis of microscopic hair comparisons — was all but ignored by other courts. In Johnson v. Commonwealth (1999), the Kentucky Supreme Court upheld the admissibility of hair evidence, taking “judicial notice” of its reliability and thus implicitly finding its validity indisputable. Other courts echoed Johnson, not Williamson. Indeed, ten years after Williamson was decided, a 2005 decision by the Connecticut Supreme Court observed (correctly) that “[t]he overwhelming majority of courts have deemed such evidence admissible.”
It was only a few years ago that the FBI finally admitted that its hair and fiber analysts had overstated the certainty of their claims in virtually every case in which they had testified. Those analysts also trained countless other state and local analysts across the country in the same methods.
Read more from Radley Balko @ the Washington Post