Fingerprints Recoverable From Cleaned Metal

dstates points out a recent article from guardian.co.uk which discusses a new method by which to recover fingerprints from metal. The method relies on corrosion caused by sweat and other biological residues on the metal's surface. Quoting: "The patterns of corrosion remain even after the surface has been cleaned, heated to 600C or even painted over. This means that traces of fingerprints stay on the metal long after the residue from a person's finger has gone. The chemical basis of the change is not yet clear, but [Dr. John Bond] believes it is corrosion by chloride ions from the salt in sweat. These produce lines of corrosion along the ridges of the fingerprint residue. When the metal is heated, for example in a bomb blast or when a gun is fired, the chemical reaction actually speeds up and makes the corrosion more pronounced."

I wonder

[oodaloop]

how many peices of evidence for earlier crimes we can now find a print where we couldn't before? Maybe solve an unsolved crime or two, or free someone innocent? The ramifications for Iraq alone where we can match prints on IED remnants to current detainees is enough to keep me interested.

Too Bad Fingerprinting is Useless

[good soldier svejk]

At least as it is currently practiced. [wikipedia.org]

Re:How Long Do They Have to be There

[Anonymous Coward]

A good print would presumably require a good surface finish, bullet casings are rolled from sheet I don't imagine you'd get a print of a knurled finish. The article says brass corrodes well, yet copper and zinc both have high resistance to corrosion -- but perhaps not so with chlorides? Furthermore water based cutting coolants are corrosive (and not everything is well cleaned after manufacture), to say nothing about objects that are chromed/lacquered for decorative or protective finish.

Archaeology Applications

[xdancergirlx]

Does this mean that we can see the fingerprints of people that handled old metal objects/chalices/swords/etc.? Maybe it would just be an item of curiousity to have a copy of Julius Ceasar's or Queen Elizabeth's fingerprints but I would put it on my wall! Maybe we could learn something about how fingerprints have changed (or not) over the course of history.

Re:I wonder

[Ucklak]

Except now we're all going to be fingerprinted so they can match these rogue fingerprints.

Re:I wonder

[badran]

I wonder how many fingerprints can be gathered from the remains of a pipe from some IED that was forged from junk and derby. I guess you can even find a print from a plumber who installed that pipe under the sink? Or a print of a shop keeper who was selling pipes, does it make him a bad person?? What if that person was detained for some reason?? Now with a print from a pipe that he sold is will be shipped to some remote location and,,,,,

corrosion? how much?

[Luke_22]

Great method, ok, but i dubt it works for everyone.

ok, we all have some corrosive sweat or alike in our skin, but that doesn't mean we all drop out the same amount of corrosive liquid.

there are people who can not touch a motherboard 'cause it would end with a big mark on the metal, it could even lead to malfunction, this is well known in the industry... I guess they borrowed their idea from here...

but how much of this corrosive is required for this method to work?
also, saying "metal" is saying all and nothing... there are metals that corrode easily, others that don't...

Re:I wonder

[mikael]

Just imagine all the suspects involved with fingerprints on the brass cartridges:

1. The packing person who took the cartridges and placed them in a cardboard box.

2. The shop owner who took the cartridge out of the box to ensure it was a match with what the customer wanted.

3. The actual person who loaded the weapon.

If one fingerprint overwrites another, then it's not a problem. But what if the corrosion effect is additive and you get two patterns merged together. Would forensic experts be able to separate the two or would they get false positives with other fingerprints of innocent people?

Corrosion is a complicated subject

[Kupfernigk]

I have actually done research into chloride corrosion of brasses, and the answer is that it is enormously variable. Whether the brass is turned or stamped, the temperature, the number of steps in the stamping process, the sharpness of turning tools, the final treatment (grind to size, polish etc.) all affect the rate of attack. One would expect much the same for other metals, though considerable research would be needed. This will probably become a nice little earner for expert witnesses.

Re:corrosion? how much?

[TheRaven64]

I don't know the details of this particular technique, but I recently came across an approach to getting fingerprints from fired bullet casings developed by some guys at Swansea which relied on Van der Waals forces - the amount of contact required is very small.

Re:I wonder

[muridae]

"That being said, it is far worse to convict an innocent individual than to let a guilty man go free."

At a one/one ratio, but some friendly casualties are inevitable. We accept a certain baseline of victims and injured/KIA police as the cost of fighting crime. We also tacitly accept a few wrongful convictions...

When does the ratio become acceptable or unacceptable? At 10:1; 1:1; 1:1,000,000 or at either extreme, "Even the innocent should be jailed if it means we catch all the guilty people." or "The guilty should go free rather then an innocent person be jailed."

Re:Problem solved for criminals:

[srmalloy]

If you're going to police the area for your spent brass after you shoot someone, you're better off using a revolver, which won't toss empty cartridges all over the place. Beyond that, if you're doing it someplace where you don't already have your prints all over the place, thin gloves will keep you from leaving fingerprints in the first place... and you can dispose of the spent brass and gloves in widely-scattered places unrelated to the crime. If you're near the ocean, toss them in; the effect of the ions in the salt water will make any residual markings on the brass unrecoverable fairly quickly.