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."

Plastic weapons

[Anonymous Coward]

This will open up the renaissance of plastic weapons.

How Long Do They Have to be There

[theshowmecanuck]

How long do the fingerprints have to be on the metal to corrode it enough to get a good fingerprint from this method? For example, if the perpetrator uses a cloth to wipe the fingerprints off the metal immediately after the crime, will the metal have corroded enough to still give a fingerprint by this method? Or do the fingerprints need to be there for some time in order to corrode the metal enough to give a good print? And if they wipe the fingerprints off is there still enough residue to still corrode the metal, or will they need to wipe the fingerprints off using some sort of solvent or cleaner? etc. etc. etc. It would be interesting to here more.

Re:I wonder

[txoof]

That's a really good question; it could be a huge boon for unsolved cases, vindicating wrongfully convicted individuals. I could also be a huge disaster for police departments. Thousands upon thousands of individuals appealing for reexamination of fingerprint evidence could swamp crime labs.

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

Re:Too Bad Fingerprinting is Useless

[Kneo24]

From what I gather there, it's not the methodology that's at fault, it's human error. Perhaps they need better training? In the end I wouldn't say that what we currently have is useless, but only that we should trust those examining the fingerprints a little less, perhaps.

Passvation layers?

[gboss]

What about metals with passivation layers, such as aluminum, titanium, and stainless steel? TFA does not address this at all... Sure, brass may be the main metal that they are going to need for shell casings, but a lot of guns are made with stainless steel.

Re:Plastic weapons

[shadow349]

This will open up the renaissance of plastic weapons.

Or, you know, gloves.

Seeing the wood for the trees

[Hognoxious]

If the fingerprints are that persistent, then lots of other marks are going to be there too - probably including lots of other fingerprints. The hard part's not going to be detecting the prints, but separating the relevant ones out from the rest of the item's history.

Re:I wonder

[Vellmont]

how many peices of evidence for earlier crimes we can now find a print where we couldn't before?

How many pieces of evidence are now ruined, because there wasn't a careful procedure followed in the chain of evidence where nobody touched it? A bullet casing or bomb fragment being criss-crossed with fingerprints isn't exactly going to make this technique any easier.

Re:I wonder

[cluckshot]

This really drives one to another issue. The longevity of the fingerprints will remove their value. All a finger print proves is proximity. As long as a finger print is there, it proves nothing but attendance. If it was a bio-subtance it had a short life span making it not only presence in definition but also proximity in time. That made finger prints useful. The problem here is that these now become "Undated" finger prints and as such unable to be related to events which was their only value in crime ID other than to have a list of suspects. This points out the most amazing reality about the crime "proof" we see in labs today. For the most part science is destroying evidence entirely. For example: Photos once were valuable. Then retouching started. Then it went to digital where retouching could be infinite. In the end, a photo is little more than fiction in court. Sound prints same. Now we see the ability of the police to fabricate evidence against someone to fullest extent unless we all are aware of what can be done.

Re:I wonder

[couchslug]

"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...

Or salted lemon wet naps

[spineboy]

I mean come on - not too hard to get around, but still it's interesting.

Re:I wonder

[Dorceon]

Of course the ability to find old fingerprints doesn't mean it's no longer possible to dust for prints the traditional way. You know, the way that does prove proximity in time?

Re:I wonder

[Digital End]

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

Tell that to the next rape victom.

Life isn't black and white, I loath short high and mighty quotes that try to paint it that way.

Re:NaCl

[Arimus]

Err... expensive? buy a tub of marine salt (the kind you use to mix for marine fish tanks) and dump the weapon in that for a few weeks - ideally heated and then place in a bag and leave to corrode...

Re:I wonder

[couchslug]

My "feelings" are not relevant to the facts, which I noted above. While it is the duty of law enforcement to try to avoid punishing the wrong people, it is not rational to expect that it will never happen.

I would be trying everything I could to get any wrongful conviction reversed, but I would still understand that ALL processes have an error rate which, while it can be reduced, cannot always be reduced to zero.

Re:Plastic weapons

[mabhatter654]

it would seem to be only circumstantial evidence though.. nearly every person who fired the gun would leave a "permanent" fingerprint. That would reduce the utility of this. I suppose what they're after is damaged metals though. Like from bombs or car crashes during persuit to be able to figure out who the guy working on the metal was when he's cinders.

Re:I wonder

[JesseMcDonald]

Perhaps a better question would be: are you willing to take the risk that the person you're locking up may later be proven innocent, knowing that if that happens you'll have to pay restitution for all the pain and suffering you've caused them (not to mention lost wages, etc.)?

The "correct" balance between false positive vs. false negatives is far too abstract to have any objective answer. This is a situation that calls for a feedback loop, punishment in proportion to the effects of an incorrect judgment. The standard of evidence would then take care of itself. In any event, it is only right that one make up for harm done to others, even when one thought one was doing the right thing at the time.

Re:I wonder

[garett_spencley]

"We also tacitly accept a few wrongful convictions..."

Speak for yourself.

Re:I wonder

[keeboo]

but I'd risk an innocent to keep in a rapist/murderer

Try stating that once you're the innocent in question.

Re:I wonder

[Headw1nd]

I'll bite, because we don't need lofty quotes to prove it's worse to convict an innocent man than let a guilty man go free, I can do it with simple algebra.

Let's take the harm suffered by letting a guilty party go free. We can call it G. We will assume this is a positive value, since I think we can agree that letting guilty people go free is harmful to society.

Now, let's take the harm of imprisoning an innocent man, which we will call I. Also positive, since putting an otherwise useful member of society in jail for no reason is something I think we'll agree is harmful.

So let's look at the harm caused by each of our actions. Letting a guilty man free is of course G, as by our previous definition. Now to calculate the value of imprisoning an innocent man, we take our value I, and add G. Why? Well, in convicting the wrong man, we have inherently allowed the guilty party to go unpunished. So we can conclude that that G is less than I + G, i.e. it is better let a guilty man go free than to punish an innocent man.

Didn't think of that, did you?

So while convicting an innocent man might give you the opportunity to go tell that rape victim, "It's ok, we got him" it's a lie, and that lie not only destroys an innocent mans life, it lets the real rapist go free.

Re:Plastic weapons

[nospam007]

Or perhaps it will cause criminals to start taking better care of their guns. A well oiled gun won't have this problem.

Or use stainless steel guns.

I guess the most impact could be if they could check guns from unsolved crimes from the last 50 years, if no dumbwit copa handled them without gloves that is.

Re:More forensic 'science' vaporware

[lpangelrob]

As my lawyer friend says... the court of law doesn't necessarily judge based on who actually did the crime. It judges on who has the better story.

That said, the story still has to be based on a fact.