Print Examination of Skin
by Ed GermanBecause the same chemicals naturally deposited in latent prints are also present on the rest of the body's skin, successful latent print detection on skin normally involves a contaminant of some type (blood, dirt, lipstick, wet paint, vaseline, etc.). I recommend detectives look carefully at the victim's skin for any obvious "finger or palm ridge detail" (not just red marks on the skin). Success may come in the form of just having your evidence technicians take pictures of visible prints.
updated 10 July 2001
If the victim is
wearing red or orange lipstick and the suspect put his hand on her (or
his) mouth, you will have good potential for examining the live (or deceased)
victim's body (and clothing, bed sheets, etc.) with an alternate light
source or portable laser (viewing through AR goggles - typically orange)
to see latent prints which are invisible in room light/daylight but glow
brightly when excited with relatively monochromatic blue-green light.
Red and orange lipstick contain dyes very similar to those we use in crime
labs to "tag" faintly developed super glue fumed prints and make them glow
There are two schools
of thought insofar as how to develop invisible (latent) friction ridge
prints which may be on a body. They are the "lift transfer"
method and "direct super glue fuming" method. It is possible
to use both methods (lift transfer, then fuming) on cadavers, though most
experts tend to use only one or the other.
Known for decades as the "iodine fuming silver transfer lift" method, the development of fatty/waxy contaminant latent prints transferred from skin onto a nonporous surface is still quite popular... but now with improved transfer mediums and post-transfer development. Since the 1990's, super glue development of the transferred prints has generally replaced old fashioned exposure of silver plates to actinic lighting for developing impressions. Latent Print Examiner William Sampson from Florida has contributed to much of the modified transfer lift research for skin.
For live victims, a piece of black plastic (such as RC photo paper developed as black) can be held against areas suspected as possibly bearing latent (invisible) prints. Other nonporous surfaces such as a mirror, glass, or metal plate may be used instead of photo paper. Some examiners use a sponge or soft pad between their hand and the photo paper to improve contact the victim's skin.
Hold the transfer surface against the skin for 15 to 20 seconds. The nonporous transfer surface should then be super glue fumed to develop latent prints which may have transferred. There is no need to wait for "water content drying" because any water in the latent print residue will aid polymerization with super glue fumes.
After super glue fuming, further development of the nonporous transfer surface should include luminescent dye stain, laser or alternate light source excitation, and (lastly) powder rubbing.
For deceased victims, the body's skin surface should be between 72 and 80 degrees for optimal fatty/waxy impression transfer. Warm the lift card or other transfer medium with a portable hair dryer just before lifting (warming it to above 86 degrees fahrenheit has been suggested by some researchers).
Some examiners use
porous white paper (such as adding machine tape) for lifting impressions...
the main difference being the post-transfer development methods.
DFO, ninhydrin and then PD is one of the most sensitive sequences for processing
Ivan Futrell and Tim Trozzi of the FBI's Latent Fingerprint Section worked with Art Bohanan of the Knoxville, Tennessee Police Department in performing some of the most significant research of the 1990's on super glue fuming bodies.
Ideally the body should not be refrigerated prior to fuming because moisture can destroy impressions that might otherwise be developed. If already refrigerated, permit all condensation moisture to evaporate upon removing the body from the cold locker/drawer.
An airtight plastic tent can be assembled over the body and fuming is accomplished using heat acceleration (coffee cup warmers) accompanied by a small, battery powered fan to help with even fume distribution. The fan should be battery powdered because sparks from a 110V electric fan motor may pose a fire hazard in a confined fuming chamber.
A test strip of plastic or aluminum bearing a "test" latent print should always be fumed with the body. If the test impression has developed well (clearly) then you are ready to dust the body using a contrasting color powder. Feather dusters with fluorescent powders are sometimes successful; but black magnetic powder is used more often. Black magnetic powder usually "paints" the skin less, doesn't require a laser or alternate light source and is easier to photograph.
Portable fuming devices are commercially available and can be used to develop prints in as little as 10 to 15 seconds of fuming for each small area examined.