2015/09/11

Allgov September 10, 2015: FBI Errors Lead to Discovery that DNA Evidence May be Far Less Foolproof When It Includes More than One Person

Relying on DNA evidence for criminal cases is great when the evidence being tested is from only one subject. But mix in samples from multiple people and it turns out that the results are a lot more fuzzy.

The issue of testing mixed DNA arose after the Federal Bureau of Investigation (FBI) found 51 errors in its DNA database out of tens of thousands of entries, according to the blog Grits for Breakfast, which focuses on issues of Texas criminal justice.

The FBI claimed the errors were insignificant, an assessment disputed by some criminal justice experts, such as Lynn Garcia of the Texas Forensic Science Commission (FSC). Garcia found, according to the blog, “the largest discrepancy estimated from the data-entry errors would have reduced a likelihood of one in 260 billion that it belonged to another person to one in 225 billion. With seven billion people on the planet, that looked like a yawner.”

But then “some Texas prosecutors asked for their probabilities to be recalculated” and after that was performed, the numbers changed dramatically. more