Gunpowder Residue Tests Are Meaningless

[Tuckerfan]

As someone who watches shows like Forensic Files, I’ve always found the various tests used in those types of investigations fascinating. Now, it seems that one of the most often cited test is useless.

But recent studies have shown that a non-shooter can become contaminated without going near a firearm. Lubor Fojtásek and Tomás Kmjec at the Institute of Criminalistics in Prague, Czech Republic, fired test shots in a closed room and attempted to recover particles 2 metres away from the shooter. They detected “unique” particles up to 8 minutes after a shot was fired, suggesting that someone entering the scene after a shooting could have more particles on them than a shooter who runs away immediately (Forensic Science International, vol 153, p 132).

A separate study reported in 2000 by Debra Kowal and Steven Dowell at the Los Angeles county coroner’s department reported that it was also possible to be contaminated by police vehicles. Of 50 samples from the back seats of patrol cars, they found 45 contained particles “consistent” with GSR and four had “highly specific” GSR particles. What’s more, they showed that “highly specific” particles could be transferred from the hands of someone who had fired a gun to someone who had not. This doesn’t surprise Arvizu. “If I was going to go out and look for gunshot residue, police stations are the places I’d look,” she says.

I’m a little rusty on my conspiracy theories, but IIRC, they ran one of these tests on Oswald. Don’t remember what the results were, but I’m sure the tin foil hatters will find a way to twist this to their advantage.

[GIGObuster]

-blink-

I do fear opening another big can of worms, but I do remember Mumia Abu-Jamal was also convicted with this kind of evidence.

[CynicalGabe]

@GIGObuster

-blink-

I do fear opening another big can of worms, but I do remember Mumia Abu-Jamal was also convicted with this kind of evidence.

FREE MUMIA!!!
HE KILLED A COP AND HE SHOULD FRY!!!
Ok, the reasoned arguments of both sides have now been presented, hopefully we can avoid that trainwreck…

[Diceman]

Cecil wrote an article revealing how a lot of the evidence routinely used in courts rests on suprisingly shakey foundations. I can’t find it right now, thanks to our useless search engine, but I remember the jist of it well enough.

There have been a couple of cases where people were wrongly convicted because their fingerprints were very, very similar to the real criminal’s. We only know about these mistakes because the real criminal later confessed, which raises the question of just how common this sort of thing is, and how many more people are sitting in jail because their fingerprints match some scumwad’s.

Even DNA tests have some questionable aspects. Those numbers given with DNA tests (ie, “there’s a 1 in 6,000,000 chance it could be someone other than him”) are theoretically sound but have never been proven to be accurate. The real number could be one in 6 billion, or only one in 6000.

[CynicalGabe]

There was a recent case of an American lawyer being arrested in connection with the Madrid train bombings. The Spanish police faxed some fingerprints to the FBI. In transmission, the image lost quality, as faxes are wont to do. The FBI ran this through their system, and got a hit on a lawyer (In Oregon) who had done some work representing people picked up in the post-9/11 dragnet.

The Homeland Security Groupthink mentality led the FBI to go: “BINGO!”

[NurseCarmen]

IIRC, fertilizing your lawn with one of those handheld spreaders will give you a positive GSR result as well.

[lonesome_loser]

Wild ass statement here…

But if you actually fire the gun as opposed to just being in the room, would the gp be embedded deeper into your skin? And if so, is there a way to test that?

[soulmurk]

I was always under the impression that such knowledge was fairly common. I mean, just because you’ve got a couple of particles of fecal matter on you doesn’t mean you shit yourself.

The article later states:

Scientists using the technique are aware of the potential contamination problem, but how they deal with it varies. In Baltimore, for example, the police department crime lab’s protocol calls for at least one lead-barium-antimony particle and a few “consistent” particles to be found to call the sample positive for GSR. The FBI is more cautious. Its protocol states: “Because the possibility of secondary transfer exists, at least three unique particles must be detected…in order to report the subject/object/surface ‘as having been in an environment of gunshot primer residue’.”

and

Even worse, it is possible to pick up a so-called “unique” particle from an entirely different source. Industrial tools and fireworks are both capable of producing particles with a similar composition to GSR. And several studies have suggested that car mechanics are particularly at risk of being falsely accused, because some brake linings contain heavy metals and can form GSR-like particles at the temperatures reached during braking.

So, they’re aware of possible transference, false reads, and that one particle is not condemning… though it appears by the wording that the guy at the beginning of the article is being held because a particle was found on his hand, which is a load of doody.
I don’t think this makes this type of evidence useless, but it does call into question those cases which were “proven” solely based on conclusions reached with GSR evidence.

[Thalion]

The Washington State Crime Lab stopped performing GSR tests a few years ago, for the reasons stated in the linked article. If an investigation really needs a GSR test for some reason, we have to use a private lab.

[CynicalGabe]

@lonesome loser

Wild ass statement here…

But if you actually fire the gun as opposed to just being in the room, would the gp be embedded deeper into your skin? And if so, is there a way to test that?

No, because the gunpower that is ejected forcefully is ejected in the direction of the fire - e.g., away from the shooter.

[Capt.Ridley_s_Shooting_Party]

IIRC, Jill Dando’s (a minor UK celebrity) killer was convicted on the strength of gun powder residue found in his pocket. Doesn’t this finding make any conviction based on gunpowder residue tests potentially unsafe?

[soulmurk]

@CynicalGabe

No, because the gunpower that is ejected forcefully is ejected in the direction of the fire - e.g., away from the shooter.

Wouldn’t some also be ejected fairly forcibly along with the expended shell casing?

The vast majority of the residue would be pushed forward and outward (which is how they can sometimes tell how far away a gun was when it was fired), but I have to imagine that some radiates outward, and even backward, and that some is expelled along with the spent shell. And that’s presuming an enclosed room with poor ventilation… what about outside with 5mph winds?
The problem with this type of evidence is that it is only useful as a tool to show if someone were near a fired weapon, or how close or far the weapon was discharged from its target; and for those things I think it works well. Linking someone to a scene does not automatically prove they were involved in what happened, just that they were there. Their actions from there need to be determined by other investigative means.

[CynicalGabe]

Most powder reside I’ve had on me drifted back from the plume exiting the barrel. Unless a part of your body was close to the shell ejection (assuming the gun is an autoloader) there should be no forcible impact.