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."

Comments

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.

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?

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."

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.

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...

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.