DNA Evidence In Cold Cases Not So Solid As It Seems


When DNA is used in cold cases, and the samples often are incomplete or degraded and there are few other clues to go on, the reliability of DNA evidence plummets–a fact that jurors weighing such cases are almost never told, the Washington Monthly reports. As a result, DNA, a tool renowned for exonerating the innocent, may actually be putting a growing number of them behind bars. Says Dan Krane, a molecular biologist at Wright State University and a critic of the government's stance on DNA evidence: “There is a public perception that DNA profiles are black and white. The reality is that easily in half of all cases–namely, those where the samples are mixed or degraded–there is the potential for subjectivity.”

Outside scientific circles, the perilous distortion of DNA evidence has gotten little attention. This is partly because the underlying mathematics can be difficult to grasp for those with no training. There may be another factor at play: so far, those who have been swept up in cold-hit investigations have mostly been convicted felons and sex offenders, because theirs were the only profiles in the databases. The possibility that people who have committed vicious crimes might be getting shabby treatment from the courts is far less likely to stir public outrage.

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