Forensic science has become the nearly unquestioned gold standard in criminal cases. This is, in part, due to dozens of television crime dramas showing tests which are supposedly foolproof. It is also because many of these tests were developed and endorsed by agencies like the FBI.
Sadly, forensic tests once thought to be highly accurate are proving instead to be wholly unreliable. And in an announcement that could have huge implications in the world of criminal defense, the FBI recently admitted that one of its widely used tests is not, in fact, reliable, and that nearly all of its laboratory examiners using that test gave flawed testimony that unfairly aided prosecutors.
The now-debunked test is known as "microscopic hair comparison." It was essentially a test that compared highly magnified hair samples (presumably found at crime scenes) to hair samples taken from defendants.
The microscopic hair comparison unit consisted of 28 laboratory examiners, who often testified in cases involving MHC evidence. But in a review of just 268 of those cases so far, it has been revealed that "26 of the FBI Laboratory's 28 examiners overstated forensic matches, and that flawed testimony favored the prosecution more than 95 percent of the time."
Even more disturbingly, the FBI admitted that it knows of at least 32 cases where defendants were sentenced to death, based at least partially on inaccurate "expert" testimony. It is too late to save nine of those defendants, because they have already been executed.
There may be no way to know just how many innocent people have been wrongfully convicted by the pseudoscience of microscopic hair comparison. Nor can we know how many people have been wrongfully convicted by other now-debunked practices like bite-mark analysis.
One thing is clear, however: Evidence in a criminal case is almost never as rock solid as it may seem at first blush. A good criminal defense attorney knows how to challenge the evidence and even the legitimacy of forensic tests used by the prosecution.
Source: Equal Justice Initiative, "FBI Admits Flawed Forensic Testimony Affected At Least 32 Death Penalty Cases," April 29, 2015