Regarding fingerprints

Watch out

Be very careful, I see the guys on CSI now are getting fingerprints off bricks, dirt and tree bark. You better wipe that gun down real well.

It's amazing what they can do on TV, or what you can get FBI techs to testify to in court.

I've been fingerprinted a couple of times for my CHL and renewal (TX requirement ) and each time the prints were unacceptable and had to be re-done at the DPS office.

So if it's difficult to get acceptable prints from a co-operative subject using a regular fingerprint kit on a regular fingerprint card, I think it's really amazing that they can get good prints from " . . . bricks, dirt, and tree bark. . . "

(Say . . . wasn't there just another murder case where they got not a fingerprint but the perp's DNA from the murder weapon? The case where a guy murdered his wife & child and then ran off to Britain??)

From my understanding, when they attempt to match fingerprints, they are comparing points. There is no such thing as a partial print. The reason for wanting the known print toi be as good as possible is to make sure that as many points as possible can be matched.

Be carefull, fingerprints can show through latex gloves. I'd wear a pair of jersey gloves. (The kind that are $.99 a pair) Then wipe the gun. You can also oil it and that will destroy fingerprints.

CSI will find fibers from the bandana

--wally.

remember to wipe the ammo, they could get a partial thumb from when you loaded the mag

Back to your question. Yes. If you take the time and are diligent enough you can clean all of the finger prints off of the weapon.

Second, the little finger tip stickys from "Gone in 60 Seconds" would only cover the pads of your fingers and not be very helpfull. You still have to worry about palm prints. Palm prints can be used for indentification the same way finger prints can. That's why everyone that gets booked in for the first time gets full sets of finger and palm prints taken...at least here they do.

BTW, the "extra" print areas also include your writers palm (outside of hand) and your bare feet. All of your rigid frictioned skin is distinctively marked.

Finger (and other) prints are due to skin oils being transferred to the object from the skin. The skin has ridges and grooves, so the oil is transferred with a copy of those ridges and grooves. Anything that disolves the oil, or disrupts the pattern of ridges and grooves in the oil, will make the prints unreadable (that is why rubbing with a rag works - the pattern is smudged beyond recognition). If a person has very dry skin, they may not transfer enough skin oil to hold a copy of the ridges and grooves; that is why some people have a problem getting good fingerprints for their CPL application. Some police departments have applicants put hand lotion on before taking fingerprints, so thay can get a good transfer of the pattern (in the lotion, instead of skin oil).

Surfaces that absorb oil are hard to get a fingerprint off of, so masonry and unpolished wood do not provide good prints. Smooth metal, glass and polished furniture will hold prints well.

Latex gloves prevent the skin oils from being transferred to other objects, so they prevent fingerprints being left on objects that are touched. The fact that the latex gloves are thin enough to see the prints inside the glove, has nothing to do with their ability to block print transfer.

When you see the TV shows with the police dusting for fingerprints, they are applying a very small amount of fine visible powder to the oils of the fingerprint, blowing off the loose powder, and then they use a transfer agent such as an adhesive tape to collect the powder that has absorbed the skin oils in the pattern of the fingerprint.

There are other techniques that are being developed to record the pattern, that may not require as much skin oil to be transferred to the object. Just to speculate, I would expect some sort of chemical that bonds to the skin oils, and glows under ultraviolet light, that can be photographed.

Fortunately, CSI (nor anyone else) could get finger prints off of my Grandma's prize Rhode Island Red rooster after he tried to flog me.

Dip it in a vat of sulfuric acid, then wipe down with bleach, and then a torch..

and even THEN, CSI may very well get a "partial match".

My mom told me that if you aren't careful with bleach, it will burn your fingerprints off. Never quite felt like testing it, though! I would be interested to hear what results you can come up with.

As for doing anything with latex gloves, one of the fingers will break withing a couple minutes, guaranteed. I wouldn't believe that fingerprints will show through the gloves unless someone can show a source to it.

Real life story where I am; the police got their act together and caught a rapist from 10 years ago by getting DNA off some duct-tape he touched (and then going through the suspect's garbage and comparing).

Finger (and other) prints are due to skin oils being transferred to the object from the skin. The skin has ridges and grooves, so the oil is transferred with a copy of those ridges and grooves.

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This is true for Latent prints, but there are other catagories of prints. There are also Patent prints that are a result of the fingers depositing foreign material such as blood, paint, mud etc. on a surface. Then you have Molded prints that are when you touch something soft like clay, butter, wet paint and you leave an impression in the substance.

Surfaces that absorb oil are hard to get a fingerprint off of, so masonry and unpolished wood do not provide good prints. Smooth metal, glass and polished furniture will hold prints well.

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This is not true at all.

A) Surfaces that absorb oil, classified as Porous (paper, unfinished wood, cardboard), hold prints very well. The method for retrieving them is different though. There are basicly three methods for retrieving prints on Porous surfaces.

I. Iodine Fuming - The procedure involves placing a few iodine crystals in a fuming pipe, heating the pipe with a lighter or match, and blowing the iodine fumes through the mouthpiece of the pipe onto the surface. Iodine fumes are purple in color, although the prints that develop will be yellowish brown. Prints developed by this method disappear rapidly, so they must be photographed quickly. Really only works well on very fresh prints.

II. NINHYDRIN SPRAY - This is a particularly useful method for all kinds of surfaces, including books and wallpaper, and is designed to develop prints that may be very old. Ninhydrin will develop prints made over 30 years ago. Ninhydrin produces a blue-violet color on the developed print.

III. SILVER NITRATE - This involves spraying silver nitrate onto a surface (such as wood or cardboard) with an aspirator, or it can be applied with a brush or swab. After the liquid is in place on the surface, it is left to dry for about five or ten minutes, then the area is exposed to ultraviolet light, but regular bright light works just as well sometimes. This method produces a clear, crisp print because the chemical picks up on the salts in the perspiration. Prints developed this way also disappear after a short time, so lifting and analysis is done via photography.

B) Surfaces that don't absorb oil, classified Non-Porous (glass, metal, hard plastic), actually don't hold prints well due to the fact that all you have is the oil or foreign matter deposited on the surface. With no absorbtion of the oil, any physical contact will smudge the print...back to, "Yes. If you take the time and are diligent enough you can clean all of the finger prints off of the weapon."

Have the main character wear some finger cots, they're like leeetle condoms fer yer mitts!

.....
You could do a crazy-glue test yourself on some similar metal (after wiping it off) I guess.
Here's one page that explains it --
http://www.larry-adams.com/9711_2_article.htm
~

Lucky said:

My mom told me that if you aren't careful with bleach, it will burn your fingerprints off. Never quite felt like testing it, though! I would be interested to hear what results you can come up with.

As for doing anything with latex gloves, one of the fingers will break withing a couple minutes, guaranteed. I wouldn't believe that fingerprints will show through the gloves unless someone can show a source to it.

Real life story where I am; the police got their act together and caught a rapist from 10 years ago by getting DNA off some duct-tape he touched (and then going through the suspect's garbage and comparing).

Click to expand...

Bleach won't take your fingerprints away. I used to scrape scabs off poison ivy and pour bleach onto the open wounds to get rid of it. It never got rid of my fingerprints.

As for the topic....unless the book is meant to be realistic, why get into such details? If you're going for realism, have him wear gloves.

If a person has very dry skin, they may not transfer enough skin oil to hold a copy of the ridges and grooves; that is why some people have a problem getting good fingerprints for their CPL application. Some police departments have applicants put hand lotion on before taking fingerprints, so thay can get a good transfer of the pattern (in the lotion, instead of skin oil).

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Huh? When did they stop using things like ink, inkless pads, and optical scanners, and go to hand lotion?

Huh? When did they stop using things like ink, inkless pads, and optical scanners, and go to hand lotion?

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We use to use corn huskers lotion to get the pads softened before we took prints on the livescan machine. Then new machine has different plates on it so all we can use now is clear water. The lotion doesn't replace any type of printing. It merely helps soften the hands a bit for a better print.

One of the local Northern Virginia departments had so many allergic problems with the 'no ink' chemical print system (both printers and printees) they have gone back to good old ink.

I remember seeing on "Hawaii Five-O" many years ago that pineapple juice will obliterate fingerprints. Some perps were doing jobs in Honolulu and not leaving any prints. Steve McGarrett knew this little fact and traced the perps to a pineapple processing plant and subsequently busted their worthless clintons. I guess the acid in the juice reduced the clarity of the ridges on the finger and thus made then prints unuseable to the cops. Any truth to this or just TV telling lies again?

They also use cyanoacrylate(superglue) to find and lift prints in addition to other methods. There's a method of 'fuming' the stuff, the fumes are somewhat more attracted to a print on an object than the surrounding material. It both helps find a print, and makes a print that may have been to light or delicate to lift, usable.

Do this: without washing your hands or doing anything unusual, press one of your fingers against the mirror in your bathroom. You will likely leave a print. now, take a bandanna and wipe the print off. This is what your character will have to do to eliminate the print. Now, do the same thing, but instead of wiping it totally off, just wipe it once, firmly, with the bandanna. See how it badly smudges? It's now pretty much unusable to an investigator, as there's not enough ridge detail for a good comparison.

I did this in a trial once, to demonstrate how a defendnat could have handled an object for hours without ever leaving a useful print n the baggie of meth.

loki.fish said:

I used to scrape scabs off poison ivy and pour bleach onto the open wounds to get rid of it. It never got rid of my fingerprints.

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But did it work on the poison ivy?