TLDR: As it relates to firearms, fingerprinting isn’t infallible.
When I encounter a topic I’m not familiar with, I turn to people like criminologist/crime writer Jennifer Chase to fill in the gaps. This typically happens in the forensics department, and I’m happy to say she’s a terrific resource. The latest example is the issue of fingerprints and firearms. Specifically, how easy (or difficult) is it to find usable fingerprints on a gun?
As Chase, author of the Emily Stone crime fiction series, related to me in an e-mail, it can be quite a challenge.
From my internship years ago with a forensic lab that mainly dealt with fingerprints, trying to recover prints from a gun is extremely difficult and most of the time they aren’t usable or wiped clean.
My anonymous former law enforcement source confirms Chase’s astute observations, writing me to say, “From what I’ve learned over my career, recovering prints from a gun is extremely difficult. The places [they are] most easily found are on the gun magazine and on unspent shell casings — mainly in semi-auto [pistols] because people tend to press with their thumb to load the magazine — and the magazine itself because they tend to have flat surfaces and are protected by the magazine well.”
A recent article in Forensic magazine further backs this up:
The trigger of a handgun seems like a really logical place to find a fingerprint, right? Actually, experts say that the chances of finding a latent print on a gun can be as low as five percent. That’s because guns are purposely designed with rough edges and surfaces around the trigger to provide extra grip, and often guns are wiped clean or disposed of after the crime making it really hard for investigators to find a good print.
And if a fingerprint can be identified from a firearm, there’s still the chance that a match yields a false-positive. Here’s a quick clip that explains that.
Lay Off the Chips: Sweat Profiles
A better way of matching a person to a firearm, as Chase writes on her blog, is to identify the sweat profile left behind on the gun via fingerprints, rather than the fingerprints themselves. Eating more processed foods, she writes, increases salt in sweat, which leaves more corrosive bodily residue on the gun. Yes, this means the worse the diet of the shooter, the easier it is to match that person to a gun he/she used. It’s an interesting take I’d never thought of before. Read Chase’s full article here.
That doesn’t mean more traditional methods of lifting ‘prints are obsolete. Check out Lee Lofland’s primer on fingerprint evidence here for a look at how it’s done.
The Takeaway for Writing Fiction
While fingerprints can play an important role in matching people to firearms, they’re not as bulletproof as they may seem. Don’t overplay your hand when writing fiction. There are as many reasons fingerprinting won’t work as there are that it will.
Have any insights or experience with fingerprints and firearms? Be sure to leave a comment below.
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