I’m a relatively respectable citizen. Multiple felon perhaps, but certainly not dangerous.
Over the past quarter century, DNA evidence has transformed criminal justice, freeing hundreds of innocent people and helping unravel countless crimes that might otherwise have gone unsolved. It has also captivated the public imagination: the plots of popular TV crime shows often hinge on the power of DNA to crack impossible cases, which has helped to give this forensic tool an air of infallibility—a phenomenon known in criminal justice circles as “the CSI effect.” This failsafe image is not entirely unfounded, especially when it comes to traditional applications of DNA evidence.
But increasingly DNA is being used for a new purpose: to target the culprits in cold cases, where other investigative options have been exhausted. All told, U.S. law enforcement agencies have conducted more than 100,000 so-called cold-hit investigations using the federal DNA database and its state-level counterparts, which hold upward of 7.6 million offender profiles. In these instances, where the DNA is often 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. As a result, DNA, a tool renowned for exonerating the innocent, may actually be putting a growing number of them behind bars.
