March is all about Fingerprinting and Fumigating

Forensic Science - Fingerprints!

Continuing on with our Forensic Science theme, this month's blog is all about Fingerprints! 

Fingerprints are another source of evidence that crime scene tech's collect on site to later review in hope's of connecting a suspect to the crime scene.  

Fingerprints are the ridges that cover our finger pads, but we also have ridges on our palms, feet, and toes too!  All these prints are collectable forms of evidence when found at crime scenes, because all prints are unique to the owner.  Even Identical Twins will have their own set of unique prints between them.  

However most prints are more than just a ridge smudge left behind by your body.  Our skin is covered in pores that produce varying amounts of oils.  Our pads (hands/feet) produce a high amount of oil which covers print ridges.  When we touch a surface, the ridge marks are transferred to the surface via the oil exchange.  Our oils will adhere (stick like glue) to just about any surface, meaning we leave unseen traces of our presence everywhere we go.  These unseen prints, called Latent Prints, are thus a very good form of evidence or registration ID because they can be easily collected and are unique to each individual. 

Unknown fingerprints collected must be analyzed for specific character traits in order to compare them to a known fingerprint.  The processionals have to ID approximately 16 unique traits in a print before it can be submitted for comparison to known prints. 

Fingerprints can be found at approximately 67% of crime scenes in the United States.  Sadly, even with fingerprint evidence, only about 37% of fingerprints found can be ID'd and connected to a suspect.  This is either because of poor prints with minimal characteristics available to ID, or because unknown prints have no match when entered into the AFIS database (Automated Fingerprint Identification System).  AFIS does not analyze prints, it simply matches the print submitted by a professional Latent Print Examiner to a matching print in the database - if it exists yet.  

Fingerprints are collected in AFIS for several reasons.  Most often, prints are entered because  a person has been arrested.  Note that even if you are never charged, most likely your prints will still go into the system.  Another reason might be for a job.  Federal law enforcement officers must submit their prints as part of the job application process.  A third reason might be for a special licensing, like a concealed carry license.  Regardless of how they get there, once entered, your prints remain on file forever, just in case!  

TRY IT: Want a quick way to read your fingerprints from home?  Grab a #2 pencil, white sheet of paper, and a (white) balloon.  Use the pencil to shade a very dark box on the paper, about the size of a US Postal Stamp.  When nice and dark, place your finger (thumb) on the shading and roll it across to transfer the lead to your finger.  Blow up the balloon with 1 puff and press your darkened finger against the balloon to transfer your print to the rubber surface.  Then blow up the balloon a little bigger to grow the print for easy viewing.  Use the key above to see how many character traits you can ID in your print/s.  

Fumigation Chamber

One cool method of visualizing latent prints is by using a fumigation chamber.  The chamber is an enclosed area that items with unseen prints can be placed in.  Using a special chemical, heat, and humidity, we create a gaseous environment inside the chamber that allows the air born chemical to bind to the oils left behind on the prints.  This causes the print to 'pop out' visually and be easier to collect for later examination.

The pros have very high tech chambers, but we had fun making our own fumigation chamber and tested it out to show you how it works. 

Can you see the prints left behind on the Pepsi can and foil?

Forensic Science is a fascinating field of study and fingerprinting is only 1 small part of the field.  We hope you enjoyed this peek into crime scene investigations!

Until next time, keep on STEMing!