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Collecting DNA: A Primer

A few weeks ago, I came across a well-written article about new anti-burglary tools in the San Diego Union-Tribune , and it got me thinking about how police use DNA evidence during non-violent, so-called "lesser felony" crime investigations. We've all seen our share of crime-related TV shows and movies in which a team of detectives carefully scrutinizes the crime scene of a celebrity double-homicide or a high-profile sexual assault. This isn't much different. To be sure, this type of work is not going to be the premise of a CSI series; however, it's a valuable way to catch criminals. As Mike Grubb, the crime lab manager for the SDPD, discussed on These Days , it's unlikely that a burglar or a robber is a one-time offender. Statistics suggest he's right. According to Patrick O'Donnell - supervisor of the SDPD crime lab's DNA unit - investigators can match the suspect of one burglary case to that of another unsolved case about one of every three cases. Furthermore, some of these criminals graduate to more serious crimes, like the ones we see on CSI.

As one might expect, these investigators analyze clothing, saliva, hair, blood, and tools the criminals leave behind. Oh yeah, and urine. That's right, burglars sometimes relieve themselves and neglect to flush. Collecting DNA via human waste is more complicated and labor-intensive, but it works. O'Donnell cites a case in which a copper thief urinated in a bottle and left it behind. The DNA crime lab unit analyzed it, tested the sample against the DNA database, and eventually made an arrest.

During the course of producing this segment, I wondered if we were giving criminals a crash course on what they should not leave behind while taking stuff that doesn't belong to them. Of course, our mission at KPBS has never been the facilitation of criminal behavior. That being said, informing the public of an effective crime-fighting tool outweighs the knowledge gained by criminals. Plus, who knows - perhaps those criminals will think twice before breaking the law next time.


- Nick Stoffel is a producer for These Days and an associate producer for Editors Roundtable . Please read our guidelines before posting comments.