Processing Fired Cartridge Casings

[gherrera]

My agency is considering the discontinuance of fingerprint processing of fired cartridge casings. The thought process behind this is that positive results of this practice does not warrant the time and resources expended. Considering the high combustion gas temperature and limited surface area of this type of evidence, it has been our experience that identifiable ridge detail resulting from processing this type of evidence is almost negligible. Are there any other agencies out there that have established policies to discontinue processing this type of evidence? Any feedback would be greatly appreciated.

[Dogma]

A number of years ago, I conducted some research, in house, regarding this question. You are correct about the destructive nature of the high combustion temperatures. But it is not just a matter of “baking off” the residue. When the cartridge is fired, the heat causes the casing to expand. This places the casing in very tight contact with the barrel. Ejecting the expanding cartridge pretty much “wipes off” any fingerprint residue. However, a lot depends on the make up of the metal casing as well as the habits of the possessor of the gun. Many gang members engage in “play” with their guns, loading and unloading and dry firing them repeatedly. If they handle brass cartridges that don’t have a protective coating, their prints may be “etched” in the brass and survive the combustion. Prints put on the casing after firing are recoverable. With some revolvers, the expanding cartridge casing may resist ejection and have to be pulled out of the chamber. If an automatic pistol misfires, the casing may be caught in the ejection port and have to be manually removed.
As far as the size of the casing, .22 cal are not likely to produce sufficient quantity of detail for analysis. .25 cal, you may get lucky. .32 cal and larger, there is plenty of surface area for ridge detail.
My suggestion is to continue processing this type of evidence. It lends itself to bulk processing techniques and if successful, produces invaluable evidence.

[W. Sampson]

As pointed out by Dogma the heat probably will not destroy the print. We too conducted experimentation and had the same results as did Dogma. You are dealing with two types of casings. Semi auto and revolver for the most part. Depending on the type and composistion of the casing, the best chance is from a revolver casing. Other casings such as shot gun shells and rifle also have good potential for recovering prints both fired and unfired.

What process are you using that takes so much time?

:roll:

[Charles Parker]

I have processed a number of casings over the years and never have developed a latent print on a casing. I have on a cartridge now and then but no casing.

Then in late 2000, I recevied a S&W revolver from a murder. It contained five cartridges and one casing (all nickel plated). I mentioned to the LPE that was with me that we would go through the motions but not to expect anything. Lo and behold a single latent print was developed on the casing. I thought that it would be the investigator who pulled it out of the chamber and then put it back. Upon comparing it to the suspect an identification was made. I was amazed.

There are a number of items that will yield poor results or be difficult to process. I do not think we should shy away from these because of that.

I would suggest to continue processing them.

[dsollitti]

I've seen a method on brass shells where subjecting them to a mixture of hydrogen peroxide and vinegar causes the latent to "etch" itself into the brass. I'm playing with the exact mixture formula. Any insight?

[William Pepsis]

I heartedly agree with Charles suggestion to continue processing your cartridges and fired cartridge cases.

Our primary duty as a Crime Scene Analyst is to analyze, collect and process evidence to prove or disprove an offense has occurred. To purposely skip processing steps for whatever reason leaves another door open for the defense to question whether you are actually unbiased or processing with preconceived notions about the outcome. The suspect who attempts to "police his brass" after an offense and unintentionally drops one or more of these fired cartridge cases when fleeing may have left a fingerprint matrix behind. The possibility of an "etched" print is very real on brass, and it must be noted that it may not have fully developed when first observed. The aformentioned "malfuntion" resulting in physical handling to clear the weapon, and Charles "revolver" incident only serve to reinforce that possibilities do exist for positive development. I feel very comfortable using a cliche' that drives home the point for me... "In crime scene work you tend not to get in trouble for the things you do, but rather the things you do not do. Simplistic, but in my career I have found it to be very true.

I also am curious about the processes being used that are causing "time" factor issues.

[GatorCSI]

I've seen a method on brass shells where subjecting them to a mixture of hydrogen peroxide and vinegar causes the latent to "etch" itself into the brass. I'm playing with the exact mixture formula. Any insight?

Check out Chesapeake Bay Division of the IAI's info on this technique if you'd like - http://www.cbdiai.org/Reagents/h2o2.html

Good luck and let us know the results!

Teri DeWitt
Hillsborough County Sheriff's Office
Tampa, Florida

[GatorCSI]

I mentioned before about trying different things to develop prints on casings, and was wondering if anyone has tried and gotten prints with:

Gentian Violet
Iodine fuming
SPR
Sudan Black
Ninhydrin?

I know these are WAY out there as far as things to try, but you never know...

Teri DeWitt
Hillsborough County Sheriff's Office
Tampa, FL

[Whisler]

Just since we were throwing out brass techniques, and I didn't have a contact for dsollitti, besides the Acidified Hydrogen Peroxide, try this one:
Two formulas can be made:

Formula 44/40 (Instant Gun Blue)
1 part reagent to
80 parts distilled water
- or -
Outer's Gun Blue
1 part reagent to
40 parts distilled water

Mix either product to the specified working solution.
Lightly fume the cartridges or brass product. Immerse brass items in the solution. Turn to ensure even application to all sides. When prints begin to develop, remove brass from solution and immerse in distilled water for at least 2 minutes. Remove from water and air dry.

[GatorCSI]

One thing to add about the gun bluing - since it is an acid, keep the primer end out of the mix if you want the firearms people to be able to do comparison. The acid can change the microscopic details. We just hold the casing with non-reactive tongs and keep the primer end out. Dropping it in the water afterwards is no problem though.