Solving a crime wave with DNA

I may be one of the few people in the world of TV watchers who has never seen a single episode of CSI: Whatever, a show featuring (I am told) "scientific" forensics work. Mrs. R., however, is fond of watching another show, Bones, which features a forensic anthropologist who works with a team that routinely accomlishes astounding feats of scientific detection (example: "That bug we found on the corpse is found only in a parking lot across from a school in Arlington, Virginia. Let's go. The new kidnap victim is probably there.") They can also reconstruct faces from fragments of skull bone and entire wardrobes using some kind of holograph. Cause of death? No problem. The weapon was about 6 inches with a point an threads, swung with a force of 6 Newtons by someone who was at least 6 foot two and left handed.) You get the idea. The science is preposterous. But there remains a widespread opinion that scientific forensics can now work miracles. The poster child for that is DNA evidence.

There is no doubt that DNA evidence has been pivotal in preventing many wrongfully convicted people from being executed. The science indeed has a solid foundation *unlike much other forensic techniques, like fingerprint identification, blood spatter evidence and fiber analysis), but like any kind of science it is only as good as the system that uses it. Recently we learned of a particularly dramatic case in point involving a crime task force of several hundred desperately hunting a murderer whose DNA had been left at 17 different crime scenes. Except for the DNA, tentatively identified as from a woman of Easter European origin, there seemed to be nothing tying all the crimes together: a couple of murders, a car jacking, break ins, a domestic dispute where a gun was fired, etc. But the DNA evidence seemed incontrovertible. And how the police think they have their . . . thing:

Alarmed by the apparent randomness of the crimes, involving both highly professional work and seemingly amateur break-ins, they started checking for contaminations in the labwork. The likeliest suspect now are the cotton swabs used to collect evidence at the crime scene. All the swabs used in the forensics works were sourced from the same supplier, a company in northern Germany that employs several eastern-European women that would fit the profile. Even more inciminating, the state of Bavaria lies right in the center of the crimes’ locations, without ever finding matching DNA in crimes on its territory. Guess what: they get their cotton swabs from a different supplier.

While the suspicion had already been growing in the last few months, the smoking gun apparently was a case where they tried to match a burned (male) corpse to DNA collected from fingerprint samples an asylum-seeker had given a few months earlier. The first test showed a match between those fingerprints and the Phantom’s DNA while a second test did not. (Science and Stuff, h/t Boingboing)

DNA evidence is fallible on its own (although it is much more reliable than most other forensic evidence) and also as fallible as the humans who collect it and analyze it and interpret it. Which is to say, pretty fallible.