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LASTING IMPRESSIONS

In a previous piece, I questioned the advisability of handling crime- scene objects, as they do regularly on television, while wearing gloves. It seemed to me and several commenters that this would damage if not destroy any fingerprints that might be present. Subsequent research supports this assumption. Experts state that touching objects such as a gun, knife, bottle, credit card, etc. where fingerprint impressions might reside can indeed destroy prints. Objects, such as paper, that absorb the residue of fingerprints can be handled with gloves or a handkerchief provided they are not contaminated with anything, for example, oil, that could also be absorbed by the object.

How many times have we watched television investigators drop nonporous objects into plastic bags? Don’t do that either, say the experts. Fingerprints reside on the surfaces of nonporous materials such as metal, glass and plastic and are fragile. How many times have we watched the investigators dust hard, nonporous surfaces with fingerprint powder? The slightest contact by a bag or almost anything else - including a fingerprint powder application brush - can destroy prints. The experts recommend placing bottles, for example, in boxes so that they extend from one corner to a diagonally opposite corner, where they will be secure and prints are not likely to be touched. Ideally, they recommend that objects be treated with cyanoacrylate fumes before being transported.

Fingerprint residues reacts with cyanoacrylate fumes and atmospheric water vapor to create a white powder known as polycyanoacrylate. The powder traces the configuration of fingerprint ridges and makes hard, white, visible impressions that can be photographed, processed and recorded. Prints can be further enhanced by applying a luminescent or nonluminescent stain.

Those who have watched evidence suspected of bearing a fingerprint being fumed on television in a state-of-the-art CSI laboratory fuming chamber might wonder just how someone examining a crime scene could possibly do that at the scene to preserve prints. A recent CSI segment showed an investigator setting up a collapsible, rectangular tent over a woman’s body to expose fingerprints lrft on her skin. (Fingerprints, usually contaminated prints involving body fluids, lipstick, etc.,transferred to a surface by fingers, can be retrieved from a body’s surface. Today, fingerprints can be harvested even from such items as cigarettes, fruit, stones, bed sheets and many more materials - any surface that is about as smooth as the ridged surface of your fingers.) In the absence of such specialized equipment, fuming can still be done without too much trouble.

If you were a character in one of your stories, investigating a crime scene located far from a lab, you would need a cardboard box, or a similar enclosure, to serve as a fuming chamber and a small supply of cyanoacrylate to provide fumes. Cyanoacrylate can be found in many stores, sold under the trade names of Superglue and Krazy Glue. A simple cup of hot water, or a handy cup of hot coffee, could serve to provide water vapor. Some aluminum foil could be used to support a half-inch-diameter pool of the glue, and a piece of string could serve to suspend a suspected object, say, a pistol, in the box.

It would be preferable to have a warming device, such as a 65-watt light bulb or an electric coffee-warming coil (never a hotplate), to speed evaporation of the glue. To provide a monitoring device, rub a finger along a side of your nose to pick up some oil, and roll the finger on a piece of the aluminum foil to create a test fingerprint.

Bend another piece of foil to form a pan-shaped platform just above the light bulb or heating coil and squeeze the measure of glue onto it. Make certain neither the bulb nor the coil is touching the cardboard, close the box and switch on the light or coil. After ten minutes, check the test fingerprint. If it has not developed, continue fuming.

Two important things to keep in mind are:

(1) Fume only in a well ventilated area, and

(2) If you use a cup of coffee to humidify the fuming chamber, DO NOT drink it afterward. The prefix, cyan, in cyanoacrylate is the same prefix that appears in cyanide.

Another thing that puzzles many CSI viewers is why investigators run around in dark rooms with flashlights when they could easily turn on lights. Light from a single source, shown at an angle, often exposes fingerprints that aren’t readily visible under general lighting. Such a technique is also handy for finding footprints on dusty floors. Using laser lights that emit light of only certain wavelengths make some prints glow. Luminol is a chemical that exhibits chemiluminescence when it is mixed with an appropriate oxidizing agent. It is sometimes sprayed onto areas where the presence of blood is suspected. Even if the area has been cleaned, blood traces will often be revealed by a striking blue glow. It’s the iron in blood that catalyzes a chemical reaction that results in the glow. The glow is observable in a fairly dark room. It lasts about 30 seconds and can be photographed with a camera capable of timed exposures.

What is not usually mentioned in television shows is the fact that luminol also fluoresces in the presence of copper and its alloys, Even horseradish, feces and certain bleaches will cause a glow. In fact, bleach presents a big problem. It can make an entire, bleach-cleaned room glow, thus obscuring any trace of blood. Fortunately, DNA can still be extracted from samples after they have been treated with luminol.

Of interest but of only passing relevance to the subject matter of this essay is the fact that, in addition to humans and other primates, koalas have fingerprints. In fact, their fingerprints are reportedly difficult to distinguish from those of humans. Also of interest is the fact that koalas have front paws with five digits, two of which are opposable, like thumbs, to the remaining three. All three remaining digits have claws. The rear paws also have five digits. One is broad and opposable, like a thumb, to the others, but it is clawless. The next two digits are fused together and have two claws. The remaining digits each have one claw.

Happy holidays to everyone.

RCJ

Related posts:

1. THE CREATURE
2. Details
3. FORENSICS 108: COMPARISONS

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