Wednesday, March 28, 2007

Civilian Policy Academy 4 - It's not what you see on TV

Last night's class was forensics. Nope, not the glitzy television CSI stuff, but the way things really work.

First up -- Fingerprint Analysis. The Orange County Sheriff's Office has two latent print analysts. Our speaker has been doing this for well over twenty years, and he knows his prints. We learned about the way prints are collected, the controls to make sure the chain of evidence isn't broken (it's all about what will stand up in court), as well as the history of fingerprinting. There are only three categories of fingerprints (loops, whorls and arches) with sub categories bringing the total up to 8. Before computers, the print cards were filed according to category, and a good analyst could match a print in twenty minutes.

Myth: If a cop finds a fingerprint at a scene, it's run through a magic database and the owner is identified.

Reality: There is no magic database. Yes, there are databases where prints are filed, but these tend to be local, and the prints in them belong to people who have criminal records. If you've been fingerprinted for work, that doesn't put your prints into that file. And unless the crime is a major one, the odds are slim that the cops are going to look beyond their own local files. As Tony, our speaker, pointed out -- most of the crime in Orange County is committed by people who live in Orange County.

And about those computers. Forget what you see on TV. There's no fancy screen display that flashes "MATCH" and pulls up a picture of the suspect. What the computer gives is a ranked list of "possible matches" and a picture of the fingerprint that goes with it. Human intervention is required to decide which of the possible matches is the true owner of the print. Tony said that in once case, the actual print was choice number 14 out of 18 the computer provided. Which boils down to the computer having made 13 "wrong" matches before it found the right one.

Next post: What goes on in the lab -- and what to CSI investigators REALLY wear on the job!


Marianne Arkins said...

Interesting stuff... you must be having a wonderful time!

So, you mean all that cool stuff on NCIS is bogus? *sigh*


Terry said...

Just remind yourself, "It's entertainment."