I am enjoying re-posting these blog posts so much! It’s helping me relive my time studying crime scene analysis at SIRCHIE. If you are just joining us today, please check out Day 1, Day 2 and Day 3.
Originally posted July 12, 2012:
You are walking along the street, minding your own business. It’s a lovely summer day. The sky is blue. It’s not too hot. Birds are chirping in the air. Maybe you are love. Life is grand. Perhaps you are even whistling a happy tune.
Suddenly, a man grabs your arm. You spin around. He snatches your purse and pushes you to the ground.
You want to scream. You want to curse. You want to chase after him, but unfortunately you decided to wear your ridiculously high platform sandals today, and they aren’t conducive to chasing muggers.
Besides, you are in shock. You feel violated. You feel like this criminal can never be caught. You are angry at yourself because you never got a good look at his face. And even if you did, you are fully aware of the unreliability of eye witness testimony.
But wait a second. All is not lost.
He grabbed your arm.
He grabbed your arm!!!
Fingerprints!
So you take a deep breath. You try to remain calm, because if you start sweating, those finger prints will be lost. You reach into your back pocket, where you always carry a sheet of paper (because you also happen to be a writer.)
You press this piece of paper to your arm on the exact spot where the assailant grabbed you.
And you walk right over to the nearest police station to report the crime.
A little magnetic powder, and the fingerprints appear.
You’re probably thinking that this is impossible. But it’s not. During day 4 of the Evidence Collection Course for Writers at SIRCHIE we worked on lifting prints off of difficult surfaces, and we ran an experiment. We were able to lift prints off of skin using just a sheet of paper. In the interest of full disclosure, these prints were not entirely usable. But if your perp is really sweaty, it just might work. Timing is of the essence. Fingerprints do not stick around on skin for very long.
Skin is, perhaps, one of the most difficult surfaces off of which to lift finger prints. But what about things with texture, like the dashboard of a car? Or a wet surface? Or the sticky side of duct tape that has been used to restrain someone?
All possible.
Attempting to lift some prints.
In fact, I was actually able to lift wet prints with plenty of ridge detail off of a wet surface!
We spent the second half of today’s class learning about matching prints from Johnny Leonard, a finger print expert. We learned all about loops, archs and whorls. We learned what details to look for when attempting to match prints. We learned how AFIS (Automated Fingerprint Identification System) is used by law enforcement. It isn’t as simple as it looks on TV. You can’t just scan a finger print into the system and look for a match. The system will give you possible matches, which must still be checked by an actual human being.
We even took a test. I was able to correctly match 12 out of 16 finger prints. Not bad for my first try, but clearly I still need a lot of practice!
Studying a fingerprint.
