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By T. Christian Miller, ProPublica  FBI-seal

This story was co-published with The Atlantic.

QUANTICO, Va. — More than 30 years ago, the Federal Bureau of Investigation launched a revolutionary computer system in a bomb shelter two floors beneath the cafeteria of its national academy. Dubbed the Violent Criminal Apprehension Program, or ViCAP, it was a database designed to help catch the nation’s most violent offenders by linking together unsolved crimes. A serial rapist wielding a favorite knife in one attack might be identified when he used the same knife elsewhere. The system was rooted in the belief that some criminals’ methods were unique enough to serve as a kind of behavioral DNA — allowing identification based on how a person acted, rather than their genetic make-up.

By Ryan Gabrielson, ProPublica hairevidence

With the introduction of DNA analysis three decades ago, criminal investigations and prosecutions gained a powerful tool to link suspects to crimes through biological evidence. This field has also exposed scores of wrongful convictions, and raised serious questions about the forensic science used in building cases.

This week, The Washington Post reported the first results from a sweeping study of the FBI forensic hair comparison unit, finding that 26 of 28 examiners in the unit gave flawed testimony in more than 200 cases during the 1980s and 1990s. Examiners overstated the accuracy of their analysis in ways that aided prosecutors.