DNA Evidence Is More Fallible Than People Think

DNA testing has improved to the point where it is starting to incriminate the wrong people in some cases, experts warn. The problem is super-sensitive equipment and DNA transfer, which can lead to a person's DNA being found on a body or murder weapon even if they had only shaken hands with the real criminal or visited the crime scene, reports NBC News, quoting a column from DNA analyst Cynthia Cale in the journal Nature. New DNA kits can identify a person from even the tiniest scraps of biological material, Cale writes, but when juries are told there is a "one-in-a-quadrillion chance that the evidence retrieved from the crime scene did not come from a defendant," they aren't usually told about the possibility of transfer, she writes.

Cale—who says we "urgently need to review how DNA evidence is assessed, viewed, and described"—cites the case of an innocent man who spent months in jail after his DNA was found on a murder victim, having been transferred there by paramedics who took the man to a hospital before going to the murder scene. At the New Republic, law professor Erin Murphy describes how DNA transfer initially led police to an impossible suspect in the 2009 murder of Yale student Annie Le. After her body was found in her lab's crawl space, DNA found on her skin and underwear matched that of a convicted offender in the area. He had left DNA behind when he carried out construction work in the lab, Murphy writes, but he might still have gone to prison for the crime—if he hadn't died two years earlier. (More DNA evidence stories.)