questions about ballistic fingerprinting

[Grey_Mana]

I saw a thread (http://www.thehighroad.org/showthread.php?t=587937) that reminded me that I could ask THR folks about things I've been wondering about:

TV and movies tell me that the FBI has a database of fired ammunition for all new guns, and when the police obtain fired ammunition from a crime scene, computer and expert analysis can figure out which gun shot who. If the police suspect me, get a warrant and test fire my guns, bullet analysis will definitively say whether my gun was used in the crime.

This seems plausible for ball ammo, but I have trouble imaging this working for hollow-point. Does hollow-point ammo foil the analysis?

On the other hand, some of the non-lead type ammo seems like it would deform less than lead (which in theory would also make post-firing analysis difficult).

Out of curiosity, I was wondering how well the bullet analysis actually works.

As a citizen, I'm wondering if I need to worry about having a gun that comes up as a false positive, coincidentally having a fingerprint similar to a crime weapon. Aside from not owning the types of guns popular with criminals, is there anything a regular person can do to minimize the chances of a false positive?

Thanks.

 

[highlander 5]

I don't believe the FBI has such a data base,but some states may. If the weapon was used in a previous crime it would show up in a state data base but as far as I know there is no requirement that the FBI gets such info. There is no requirement that the FBI get the ballistics on a new firearm. Don't believe everything you see in the movies or TV most writer have a clue when it comes to info on firearms,ballistic data base,ballistic fingerprints and any other nonsense.

 

[ny32182]

Tool mark analysis is about similarities, not exact matches, such as DNA. Thus the flaw in the state-wide, "we have a case from every gun" database idea. Parts made consecutively on the same tooling will be very similar to each other. The production tooling wears and changes over time just as the gun parts will wear over time with thousands of rounds fired.

As noted, the similarities are not specific enough to match a random case/bullet to the exclusion of all others in a database of millions of guns. To find a reasonable similarity, you need to go in the other direction: start with a gun believed to be used in a crime, fire some rounds, and see if what comes out is similar to what was found at the scene.

So basically, my worries about a "false positive" would be zero. It would take FAR more than a similar ballistic match to make a conviction. It is not nearly enough as a stand-alone piece of data. This is not DNA, it is tool mark analysis.

 

[Sam1911]

Uh, wow, no. Please step away from the television.

Very few states maintain a database of fired cartridge cases from guns sold in that state. Maryland is one.

The theory here is that if the investigators recover a fired cartridge case at a crime scene, they could match that fired case against their database and perhaps tell which gun that case had been cycled through. This has problems. First off, no such database is all-inclusive, or even moderately inclusive. Only a couple or three states maintain such databases and then only for NEW guns sold in that state since the program was put into effect. So any gun from any other state, or already in that state prior to the program's inception won't be in the database.

Second, the marks left by a gun on a fired case are subject to change due to wear, and parts swapping. (Plus anyone who fires range pick-up brass would have multiple cycling marks on their cases.) This kind of ballistic fingerprinting could help point to a specific gun, but the odds are pretty long against. After an exhaustive study, Maryland State Police determined that fired-case matching was mentioned in only a very small handful of court cases, and was effective in helping solve NONE.

Now, you appear to be thinking of ballistically matching fired bullets.

There is NO ballistic database of fired bullets from guns belonging to the general population. If the police already have a gun seized in an investigation, they can fire a test round and compare that fired slug against one recovered from a body or a crime scene. Then they can say that this gun fired the round found at the scene with some decent level of certainty. (Not perfect, by a long shot.) But if they don't have a suspect's weapon, they can't produce a slug to compare.

The ballistic forensics stuff that the TV shows get wrong or where they improve upon reality is pretty extensive -- you might want to watch each show as an object lesson of what doesn't happen. Think of it as crime science-fiction. Teleporters, warp drives, Mr. Spock, and ballistic fingerprinting.

 

[bobbo]

Now, you appear to be thinking of ballistically matching fired bullets. There is NO ballistic database of fired bullets from guns belonging to the general population.

+1 this

Very few states maintain a database of fired cartridge cases from guns sold in that state. Maryland is one.

New York is the other. This has been covered quite a bit frequently (like any thread about "what's this empty casing for?"). In New York, only two "hits" on the multi-million-dollar database have come up. Neither one has led to a conviction.

Uh, wow, no. Please step away from the television.

This. CSI and NCIS are bullcrap. I'd be more worried about, since the FBI has my fingerprints from a pistol permit, of getting a false positive from somebody's fingerprints being similar to mine. How worried? I'm not. That should tell you something about how worried I am about a casing being traced back to me. BTW, I do not, and will not, own a new pistol while a NY resident until the braindead system is closed. There's plenty of used Ruger Mark IIs and S&W revolvers out there for me to choose from.

If you are worried about microstamping, another lame attempt at "solving crime" with a giant database, don't be. No state (that I know of) requires it, and the nail file on my Swiss army knife will take care of it.

 

[hermannr]

The "fired case" idea is a waste of taxpayer money, as is any other firearms registration...How many crimes are committed with a registered gun? None?, or if any, it was because the firearm was stolen from the person that it was originally registered to.

I was reading that IL was considering an ammendment to their current CC permit legislation to make the LEO's happy. I don't know what the changes might be, but think about this...the more restrictions on firearms, the more need to have LEOs...therefore, you can rest assured, whatever "changes" may be proposed, they have nothing to freedom and trust in the law abiding citizen to follow the law.

 

[Loosedhorse]

I'm glad that this fired case "finger-printing" is fading. I always thought that--since my gun, if it ever "matches" to a case found at a crime scene, will be caught by a "false positive" result--the smartest thing to do after buying a new gun in a "finger-printing" state is to take the new gun home and immediately videotape yourself polishing the chamber. Then keep the videotape with a lawyer. It will prove that any subsequent match couldn't have possibly been a valid one.

As we move into the "micro-stamping" phase, this may all start up again.

 

[kingpin008]

To answer the OP's question regarding hollowpoints foiling any attempts to compare rifiling characteristics with a known sample, have a look at the following pics:





As you can see, even though the hollowpoints are pretty well deformed, there are some remaining rifling marks. When I've watched real forensics shows, when the forensic technicians have had occasion to analyze a hollowpoint round, they've generally been able to.

So while there isn't the type of database that you thought, if there were, hollowpoint rounds would generally pose no problem in terms of analysis.

 

[jonmerritt]

They can not match a slug to a barrel of a weapon, It has been proven that they can not match it.
It is just not wanted to be known as common knowledge that forensics can not match a slug to the barrel.
There has never been a conviction (EVER) matching a slug to a barrel of a gun.
It is utter BS!

 

[CZsp01]

http://www.youtube.com/watch?v=yAlixegkf0o

 

[twofifty]

jury's propensity to believe

So we've established that analysis of case markings could provide one element of 'proof' -and a statistically unreliable one at that- in a trial by jury.

Regardless of the accuracy and reliability of the conclusions presented as fact to the jury, what remains highly problematic is the jury's propensity to believe such evidence to be conclusive.

Why wouldn't the jury assign weight and credence to this 'evidence'...after all they've seen it done on CSI.

 

[toivo]

I live in New York, a "fired case database" state. It only affects new semi-auto handguns, which means only two of the dozen handguns I own. (Maybe three, because my Glock 26 was purchased used from another New York State resident, so it probably has one filed from his original purchase of it.) The rest are revolvers or older guns purchased used. For a program like this to prove effective, it would have to be nearly universal. It also is based on a huge and flawed assumption, which is that anyone would commit a violent crime with a weapon legally registered to him/her (yeah, we have handgun registration) and would leave casings behind at the scene. Umm... no.

Why wouldn't the jury assign weight and credence to this 'evidence'...after all they've seen it done on CSI.

I've heard lawyers refer to it as "the CSI effect." Juries are much too obsessed with forensic evidence -- they convict too easily with it and are very reluctant to convict without it. You can have three credible eyewitnesses, and the jury still wants to see the little scratches on the bullet.

 

[Shadow 7D]

Go read up on the Rifle that Killed JFK, seems after so many years and test fired 'comparison' rounds, it no longer produces a similarly marked bullet as those recovered at the scene. It's a tool, and WAY over blown by TV.

 

[russ69]

We have a law in California that is on hold. Micro Stamping. It's on hold because the technology doesn't exist. It didn't stop them from passing the law though......I think they are watching to many episodes of CSI.