Confounding DNA In The Annie Le Case
Our youngest son is mid-way through medical school. At dinner the other night, he and my wife were discussing the controversy surrounding neckties in hospitals. It turns out that physicians, though scrupulous about washing their hands between patients, aren’t quite as careful with their ties. A wagging tie can transfer bacterial infection from one bed, one patient, to another. Hospitals are very dangerous places for sick people, he reported gravely. He is considering bow ties as professional attire.
I listened to this conversation as I do so many between he and my wife: they are far smarter than I am, and they worry about things that never occur to me. For decades, my role has been as the entertainment section of the family. I listened to this business of neckties and infection with a detached, almost bemused, air.
And then I stumbled upon some information in the Annie Marie Le murder case at Yale that stopped me dead in my tracks. Ms. Le, a 24-year-old graduate student at the Yale School of Medicine, was found dead, hidden behind a wall, in a campus building in September 2009. Just last week, Raymond J. Clarke, III, a lab technician employed by the university, was sentenced to 44-years imprisonment for killing her.
I confess I did not follow this case closely.
I did not know that there was a wrinkle in this case that confounded the forensic scientists. You see, when Ms. Le’s clothing was tested for the presence of DNA, there was a match found to someone other than Mr. Clarke. Analysts found foreign DNA on an undergarment of the young woman, and it matched that of a man with a criminal past.. That man was not Mr. Clarke.
DNA transfer evidence is powerful evidence. It has led to the acquittal and the conviction of those accused of crimes. What role would it play in the Le case?
None, as it turned out. The suspicious DNA belonged to man who had been dead for quite some time at the time of Ms. Le’s disappearance. There is no evidence to suggest that they ever met. But still, DNA doesn’t lie, does it? Isn’t the presence of this foreign DNA damning circumstantial evidence? It certainly would be had the man whose DNA it was not long been at the time of the crime.
DNA can be transferred from one person to another, or from one person to another object, by means of intentional or unintentional contact. Its movement from host to other is called a transfer. Once transferred, DNA can retain its molecular structure for quite some time, depending on environmental factors.
In the Le case, investigators found that the mysterious DNA belonged to a construction worker who had done work at the lab in which Ms. Le’s body was found years before the killing. Interviews with co-workers suggested that as the work progressed, workers often sweat, sometimes copiously. Some may have worked with their shirts off. Investigators concluded that the DNA in question here was transferred innocently from a construction worker to a wall or other physical object in the wall. The humidity in the room created an environment in which the cells retained their structure.
Had the DNA donor not died long before the event, his DNA would have made him a suspect. Although it is unlikely, I suppose that it is possible his DNA on a piece of the victim’s clothing might have been enough to get him charged with the crime of murder and attempted sexual assault. Imagine the difficulty of persuading a jury that he was not the killer. "His DNA is there as a result of accidental transmission," the argument would go. "Yes, he swung a hammer at the lab years ago, but he wasn’t there when a young woman was murdered. He didn’t even know Annie Le." It would have been a tough sell even though it is true.
State officials are tight-lipped about this troubling wrinkle in the now closed case. But it raises questions about our tendency to rely on DNA as a magic bullet. Sure, DNA doesn’t lie; but context is key. Given the ease with which DNA can be transferred, the Le case has me wondering whether DNA’s mere presence at the scene of a crime ought to be enough secure a conviction in cases built entirely of circumstantial evidence.
I ought really to listen more carefully to my wife and son. Small things can yield catastrophic consequences; crime scenes, like hospital beds, are easily infected.