There were clearly fundamental problems with forensic science. A 2009 report by the National Research Council, an arm of the National Academies, found that apart from DNA testing, no forensic method had been rigorously shown to consistently and reliably demonstrate a connection between evidence and a specific person.

Then, several years ago, three men from the Washington area — Kirk Odom, Santae Tribble and Donald Gates — were exonerated in separate cases. They had served more than 70 years in prison in total. In each case, F.B.I. examiners had told juries that the defendant’s hair matched hair at the crime scene, based on microscopic hair analysis. One prosecutor put the odds at perhaps one in 10 million that the hairs belonged to someone other than the defendant. (In fact, subsequent DNA testing found that none of the hair samples matched the defendant, and that one was from a dog.)

Those cases proved to be a turning point. To its credit, the Justice Department reached an agreement with the Innocence Project to review F.B.I. testimony about hair analysis in more than 2,500 cases in more than 40 states from 1985 to 1999. The results of the first 268 cases examined were reported Sunday in The Washington Post. The review found that F.B.I. testimony was fundamentally flawed in 257 of those cases — a stunning 96 percent of the total. Of those defendants, 33 received the death penalty and nine have been executed so far. Although the errors don’t necessarily mean the defendants are innocent — other evidence might have supported conviction — the F.B.I. plans to notify prosecutors and prisoners of the findings.

The problem is not limited to hair analysis. Last month, Alabama released a man from death row who had been convicted 30 years ago based solely on ballistics evidence; the state now concedes that the bullets in question did not actually match the weapon used. A few years earlier, Mississippi released two men who had been convicted of separate murders based on testimony that their teeth perfectly matched bite marks on the victims. After the true killer was later identified by DNA, experts concluded the wounds were not human bites after all but were most likely caused by crawfish and insects nibbling on the corpses.

The Justice Department, in collaboration with the National Institute of Standards and Technology, took an important step to bring rigor to forensic science in 2013 by appointing a national commission on the issue. It has had a rocky start: Judge Jed S. Rakoff, a federal judge in Manhattan, resigned from the panel in protest in January when a Justice Department official sought to limit the panel’s scope, but returned when the department reversed that approach. The commission, most of whose members are tied to law enforcement or involved in current forensic practice, now needs to listen to its independent panelists and get down to making rigorous recommendations.