Thousands of people jailed on the basis of forensic evidence could walk free as the US criminal justice system looks to bring forensics in line with modern science.

The Federal Bureau of Investigation and the US Department of Justice announced this week that they will review more than 10,000 criminal cases dating back to 1985. These are instances in which guilty verdicts were based on forensic hair and fibre analyses, along with other methods that no longer stand up to scientific scrutiny.

The review follows numerous investigations that have cast doubt on the validity of most forensic methods. Firearms and bullet analysis, for instance, can wrongly place innocent people at a crime scene.

In a strongly worded 2009 report, the US National Academy of Sciences (NAS) said that with the exception of nuclear DNA evidence, “no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual”.


But even DNA evidence is fallible: different labs can return very different results for the same sample.

Paul Cates of the Innocence Project in New York, which campaigns for people wrongly convicted on the basis of DNA evidence, says that to date, 292 people have had their conviction overturned by follow-up DNA analyses. “In half of those cases, there had been some sort of forensics problem,” he says.

Cates backs a recommendation in the NAS report, which called for a national body to set standards for forensic science so that all analysts would be consistent. “We’re hopeful that Congress will take up this cause in short order to ensure that what passes as forensics is science,” says Cates.