A Big Problem with DNA Evidence

Erin Murphy at The New Republic:

In 2009, a horrific murder occurred in a place rarely associated with violence: a Yale graduate scientific laboratory. On what was to be her wedding day, a graduate student’s body was found head down within a small mechanical chase behind a wall in the laboratory. As she fell, her underwear snagged and entangled on a vent pipe that spanned the length of the chase. Extensive DNA samples were taken from the victim, her clothing, and spaces around the chase. Testing revealed two profiles, one of which matched a co-worker later implicated in the crime through other evidence. But a second person’s DNA was also found, ominously recovered in significant quantities from samples that included the waistband of the victim’s underwear. When the profile was submitted to the DNA database, a match returned the name of a convicted offender living nearby.

Further investigation, however, turned up something mysterious. The database match suspect had died two years prior to the Yale attack. Stumped, investigators first ruled out an identical twin or other relative, as well as laboratory contamination errors. Ultimately, however, they learned that years earlier the offender had worked in construction. Specifically, he had spent one long, hot summer building the very mechanical chase in which the victim was found—and he had even made errors the first time around that required him to effectively rebuild it a second time. Even though the victim did not encounter that chase until years later, the fact that it was a space that was closed from ordinary traffic or regular cleaning, coupled with the building’s strict temperature and environmental regulation (as a result of its role as a scientific lab) helped preserve in pristine the large quantity of DNA the worker had left behind as he sweated in that space during the construction.

We're getting so good at finding DNA that even a fallen bead of sweat can lead to a DNA match. I have also pondered how easy it would be to frame somebody for a crime by getting hold of some of their hair, sweat and skin cells and strewing it liberally around the crime scene. Has this been done in a movie yet?