This gets my old forensic juices going simply because so much work is involved in the investigation and prosecution of firearms cases. Without a cooperating witness(es) your case is solely dependant on physical evidence, especially in New York State where the rules of evidence are stacked in favor of the defense.
Wiping the gun clean has long been considered best practice for villains but may soon become a quaint custom as researchers have developed a way to ‘visualise fingerprints’ even after the print itself has been removed by measuring the corrosion of the surface by deposits from the fingerprints. The technique can enhance – after firing– a fingerprint that has been deposited on a small calibre metal cartridge case before it is fired. The technique promises the ability to reopen many cases and solve cold cases around the world because the “underlying print never disappears” according to the scientists.
So when you can lift a latent (fingerprint) from a gun or cartridge casing your case is greatly strengthened. You can impeach a witness - particularly when so many witnesses (and victims) from a night club shooting or drug deal gone sour are just as big an asshole as the person doing the shooting. But it is much more difficult to impeach physical evidence. Instead, the defense attacks the premises under which the evidence was collected - the constitutionality of the seizure.
But a shell casing left at the scene is a wonderful piece of evidence. And if a latent is left on the casing, it further implicates the shooter in that it also shows intent - the sucker not only shot at the victim but even loaded the weapon. It can also implicate others in the chain of evidence, someone else stored and maintained the weapon. People with prior felony convictions are suddenly facing another felony - this time as a predicate felon - and it is amazing how much a gangbanger suddenly knows when he is facing q seven year minimum bid (flat prison term - ya gotta do the lower end before eligible for parole). We can roll these people.
The BMEWS refers to a Gizmag article:
The Incredible Indelible Latent. How sweeeet it is.
Forensic scientists at the University of Leicester, working with Northamptonshire Police, have announced a major breakthrough in crime detection which could lead to hundreds of cold cases being reopened.
Dr John Bond, Honorary Fellow at the University of Leicester and Scientific Support Manager at Northamptonshire Police said: “For the first time we can get prints from people who handled a cartridge before it was fired.”
"Wiping it down, washing it in hot soapy water makes no difference - and the heat of the shot helps the process we use.
“The procedure works by applying an electric charge to a metal - say a gun or bullet - which has been coated in a fine conducting powder, similar to that used in photocopiers.
“Even if the fingerprint has been washed off, it leaves a slight corrosion on the metal and this attracts the powder when the charge is applied, so showing up a residual fingerprint.
“The technique works on everything from bullet casings to machine guns. Even if heat vaporises normal clues, police will be able to prove who handled a particular gun.”
Dr. Bond’s initial findings, which prompted the joint study, have been announced in paper in the American Journal of Forensic Science.
The following are reproductions of latent prints. If you look closely you can see what fingerprint specialists look for when presenting latent evidence during a grand jury or courtroom proceeding. Identifying marks are:
1) ridge endings - this is where the ridge just stops. It may pick up again or turn into an island;
2) islands (or dots) - this is a minute ridge segment that occurs usually in the middle of a longer ridge segment; and
3) bifurcations - where a ridge splits into two more ridges.
This is a loop (either ulnar or radial depending on which side - inner/radial or outer/ulnar - of the wrist the loop is coming from. The fingerprint is caused by friction ridges that are actually imprinted on the top layer of underlying bone cells for your hands and feet. Friction ridges allow you to grasp objects without them slipping through your fingers.
Fingerprint residue is what the powder clings to when a CSI type dusts for prints. Fingerprint residue is comprised of water, fatty oils and amino acids. The water evaporates first. Fatty oils last a long time. Amino acids even longer. In one case a passenger in a fatal aircraft accident was identified from prints lifted from one of her school books recovered at her parents' house. She had not handled those books in over forty years.
There are much more modern methods to developing a latent print image using chemicals (super glue reacts with fingerprint residue to produce an excellent image of the latent), lasers and now some kind of variation in charge (electrostatic?) that is produced by the corrosive effects of fingerprint residue.
I experienced something like this: about three years ago I forgot to wipe down an unprotected gun barrel after handling it (my Civil War replica Model 1861 Springfield). Several months later I noticed that the residue from several of my fingerprints produced a patch of light rust that reproduced my print pattern on the barrel!
Bank robber John Dillinger had the bones of his fingers scrapped to remove the imprinting layer and then had his fingertips grafted to the sides of his chest to replace the skin cut out by the doctor. But the doctor messed up and did not scrape Dillinger's fingertip bones enough. Some ridges came through the scar tissue - enough that a positive id was made again.
This is a loop coming from the other side. About 80-85% of the population has ulnar or radial loop fingerprints.
The other type of print is a whirl. This is a whirl. See the delta on the lower left of the latent? A delta is where it looks like the ridges are flowing into the whirl. If this whirl had a delta on both sides this would be a central pocket whirl. These are fairly rare.
We had an FBI tech spend a week training us in latent identification. I was glad I never had a job like that. I would go blind.
Oops. Forgot to add this. Prosecutors like to have at least twelve points of identification for trial. But I have seen them go as low as eight.