Forensics

Jeff Sessions wants to make forensic evidence in court completely useless and invalid

Evidence regularly presented in court rooms—such as bite-mark, hair, and lead bullet analysis—that for decades have been employed by prosecutors to convict and even execute defendants are actually incapable of definitively linking an individual to a crime. Other methods, including fingerprint analysis, are less rigorous and more subjective than experts—and popular culture—let on.

But on the witness stand, experts routinely overstate the certainty of their forensic methods. In 2015, the FBI completed a review of 268 trial transcripts in which the bureau's experts used microscopic hair analysis to incriminate a defendant. The results showed that bureau experts submitted scientifically invalid testimony at least 95 percent of the time. Among those cases with faulty evidence, 33 defendants received the death penalty and 9 had been executed. No court has banned bite-mark evidence despite a consensus among scientists that the discipline is entirely subjective. One study found that forensic dentists couldn't even agree if markings were caused by human teeth. Until this month, the National Commission on Forensic Science was the most important group moving forensics into the modern scientific era.