The Justice Department and FBI have confirmed that over the course of 20 years before 2000, an FBI forensic unit had been providing false evidence against hundreds of defendants, most of whom were on trial for rape, murder, and other violent crimes nationwide.

Examiners in the FBI Laboratory's microscopic hair comparison unit were offering hair DNA analysis that incorrectly favored the prosecutors position in over 95% of the 268 trials reviewed thus far. In 32 of those cases the defendants were sentenced to death. 

The Washington Post reports: "The admissions mark a watershed in one of the country’s largest forensic scandals, highlighting the failure of the nation’s courts for decades to keep bogus scientific information from juries, legal analysts said. The question now, they said, is how state authorities and the courts will respond to findings that confirm long-suspected problems with subjective, pattern-based forensic techniques — like hair and bite-mark comparisons — that have contributed to wrongful convictions in more than one-quarter of 329 DNA-exoneration cases since 1989." 

The investigation began in 2012 after The Washington Post reported that hundreds of potentially innocent people since at least the 1970s may have been incarcerated (or executed) due to flawed forensic hair matches used as evidence. 26 of 28 FBI experts in the unit testified that the defendants' hair sample "matched" a hair sample found at the crime scene. It has been confirmed that the majority of these testimonies were based on incomplete or misleading statistics, and furthermore, no conclusive research has determined whether hair is unique to each individual in the first place. Roughly 2,500 cases have been flagged for review.