How long will fingerprints last on a surface?

kaitie · Nov 17, 2012

Working on a story and I figured out something that will totally help the plot, but I need some help sorting out how to make it work believably.

I have a character who needs to get a fingerprint discovered, but it needs to be in a weird place. My current plan is to have the character climb the outside of a building to break in, but no one really figures out how he does it until a third of the way through the book. Then someone figures out he basically spider-manned his way in and thinks to check the bricks outside the building for prints and boom, gets a good one.

In my mind, this is a brick house that has decorative bricks that stick out slightly more every so often and they can climb on those. The thing is, would something like that hold a print, especially if it's outside? Would it be better to have some kind of decorative stone thing or gargoyle at some point for him to hold onto? Would something like that hold a print better? If it's on a brick directly below a windowsill, would that protect it enough from rain that it might still be there?

WeaselFire · Nov 17, 2012

This is all variable. Surface and weather make a big difference here. If he gets his finger on some caulking or sealer under a window, it could be usable for a long time.

Jeff

mirandashell · Nov 17, 2012

I was thinking that as well. Something pliable would be best. I'm not even sure prints can be taken from stone, can they?

kaitie · Nov 17, 2012

My boyfriend suggested something like stone because it's smoother (like polished stone or marble), but it seems like smoother might mean it washes away easier?

I like the idea of it being on the brick itself, and brick can be pretty darn smooth. It's also possible that it's not something that would be useable in court. Like maybe it's a match, but not a match to a high enough degree of certainty?

All I need is enough that the FMC can figure out who he is. She's seen him before, so if she can get a list of potentials, it would be easy enough for her to figure out which is him.

mirandashell · Nov 17, 2012

Sorry, yeah, I was thinking of stone as a rough surface but marble would hold a print.

kaitie · Nov 17, 2012

What if it's on the sill? He can wipe down the top/side, but not the underside area. Who would think to check there, after all? He could easily overlook something like that, and all she'd have to do when she starts getting suspicious is lean out the window. I could easily see a good, solid thumbprint being left on the underside of the sill if he's using the sill to pull himself up.

Bing Z · Nov 17, 2012

Can he climb up the drainpipes? That's easier esp if he's not a pro burglar. That's a hell lot easier to leave prints behind, no?

kaitie · Nov 17, 2012

Might be, but also seems an easier place to wash away from. I'm trying to think of something that would still be preserved a few weeks down the line. That's why I'm thinking underside of a sill might be safe.

As for professional, he and his wife are both free climbers, so they do this sort of thing on 1000 foot cliffs for fun. I'm not too concerned about their ability to scale the wall. It's more about where would a print be preserved over time that could realistically be discovered.

jclarkdawe · Nov 17, 2012

Fingerprints result from two entirely different reasons. One is as a result of the oils on our skins, and the second is from the surface such as fresh paint. Oils will eventually evaporate and disappear. Surfaces can last forever or not, or fill in with dirt and other debris. Weather erosion from rain, dew, wind, and other natural forces can impact here.

The rougher the surface, the less likely a good print will be found, as only the tops of the surface will come in contact with the finger. Natural brick is unlikely to provide a good source for fingerprints, because they tend to come in pieces. Natural wood isn't much better, because of the roughness. Wood that has been finished with paint or lacquer can be a good source, as the paint or lacquer will fill in the wood surface.

A fresh coat of paint, even after it has dried to the touch, can still result in prints if applied with sufficient force, such as grabbing a sill to climb. This would probably be your source of prints that will last for a long enough time on an external surface.

One thing to understand is the resources police use in an investigation. For many break-ins, the police might not even bother to fingerprint. (Classic cross-examination of a police officer on why no prints at the crime scene: "Why bother to fingerprint the place. We already knew it was your client.") For a murder, on the other hand, they'll dust every surface that they have any hopes of finding prints.

Bottom line is a good job of looking for prints would reveal any print on a window sill, even underneath. But often for a break-in, the police might not bother, because a wood sill is often too rough to give good prints.

Best of luck,

Jim Clark-Dawe

kaitie · Nov 17, 2012

Well, oddly, I want something the police wouldn't catch, but that my character can go back later on and find herself (she's actually a prosecutor and for her own reasons trying to find this guy on her own).

My current logic is that the police know they'd used a rope to go out, so they assume they used a rope to come in, and there are no fingerprints anywhere else in the room because they were wearing gloves. She figures out that wearing gloves to climb would be difficult, so on a hunch goes to check out the room again and decides to check the underside of the exterior sill and hits pay dirt. Once she has it, she can have a friend run it off the record (or do it herself, perhaps) and find out who he is without the police actually knowing. Either way, it's okay if the police don't find it or don't even look (though I imagine with the person involved, they'd have to look). He's not a murderer, btw. Just a thief. :tongue

I'm thinking painted sill would probably be the way to go. Thanks for your explanation!

mirandashell · Nov 17, 2012

I think so too. Vast majority of readers will go with it. Esp those that watch CSI. According to Grissom, you can find prints on anything!

kaitie · Nov 17, 2012

Woohoo! CSI viewers for teh win.

Yeah, my main concern was readers saying "you can't fingerprint a brick" or "outside in the rain? Yeah right!" I think I can probably put in a throwaway line to appease people if I need to. Goodness knows the rest of the book is kind of crazy already.

How long will fingerprints last on a surface?

kaitie

With great power comes

WeaselFire

Benefactor Member

mirandashell

kaitie

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mirandashell

kaitie

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Bing Z

illiterate primate

kaitie

With great power comes

jclarkdawe

Feeling lucky, Query?

kaitie

With great power comes

mirandashell

kaitie

With great power comes