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Not as Certain as CSI

The addition of DNA analysis to the forensic arsenal has called the reliability of other, older methods into question, the New York Times notes in its Retro Report.

Hair analysis — matching hairs found at crime scenes to those from suspects — was often used to determine whether someone was present at a crime. For instance, the Times notes that the crime lab at the US Federal Bureau of Investigation said hairs from Kirk Odom, who was convicted of rape in 1981, were "microscopically like" one that was found on the victim's nightgown.

But as the Times notes, the reliability of hair analysis results, including in the Odom case, became murky as DNA analysis was added into the mix.

Max Houck, who used to work in the federal lab, tells the Times Retro Report that a set of hairs that forensic scientists in his unit had found to be microscopically similar were found through mitochondrial DNA analysis to belong to different people. Houck then kept track of how often the two approaches gave discordant results — which was some 11 percent of the time.

"It kind of shook us up," he says in the video.

The Innocence Project, which has cleared a number of wrongfully convicted people using DNA analysis, notes that more than a quarter of the 300 people exonerated by DNA evidence had been convicted, in part, by hair analysis.

One those exonerated people was Odom, though he was not cleared until after he served a 22-year sentence.

"This is not to say that these techniques are no good at all. Indeed, the FBI still affirms its faith in microscopic hair analysis, particularly as a first look," the Times notes. "But it now tries to follow that procedure with a deeper and more certain investigation that uses DNA sampling, and it has done so for 18 years."