Even before that, though, we need high-quality, doubly blinded trials to establish how well any of these comparison-based forensic methods actually work. Evidently, a key problem with hair comparison was that no one actually had any idea how reliable it was for "matching" a sample to a suspect. It is now obvious that the false positive rate is completely unacceptable.
We should have known this long before anyone even thought about using hair comparison evidence at trial, and the sad thing is that the experiments needed to rigorously evaluate this technique aren't even very complicated. For prosecutors, though, it is undoubtedly a lot more fun to impress juries with your scientific-sounding evidence and experts than it is to ask whether the evidence is actually reliable, and you can bet that the hair comparison "experts" were not in any hurry to show that their work was a sham.