When Bad DNA Tests Lead to False Convictions

If you’ve ever watched a prime-time crime drama like CSI, you know that DNA evidence is often the linchpin that makes a case. Match a suspect’s DNA to DNA found at the scene of a crime and it’s certain they’re the culprit. The thing is, it’s not always that simple. Most people think of DNA testing as a monolithic, infallible technique. But there are many different kinds of tests—and many different ways of interpreting them. Sometimes, somewhere between the process of collecting evidence at the scene and processing it in the lab, something goes awry.

For Chen Long-Qi, a bad DNA test derailed his life.

It was early in the morning on May 25th, 2009 and Chen was hanging out in a Taiwan warehouse he rented for work, drinking with friends. At around three in the morning, they were joined by two women. According to Chen and his lawyers, Chen left shortly after to pick up his wife from work, and sometime between 4 and 6 a.m., the two women were raped. While the victims had not accused Chen...