"Welcome to the Dungeon", fingerprint technician
The tip of the finger is far from being either smooth or symmetric. It is completely covered with tiny ridges that form a pattern that is virtually unique. Even identical twins will have different ridge patterns. It is this pattern of ridges that is called the fingerprint. When the fingertip comes in contact with something, a layer of sweat containing amino acids in the shape of the fingerprint will be left on the object. The fact that these latent prints can often be recorded combined with the fact that no two fingerprints are the same is what makes fingerprinting practical.
Fingerprinting is more involved than most people realize. In most cases it requires far more than a general dusting for prints. Dusting can only be used by itself on nonporous surfaces, and only if the prints are still fresh. Otherwise, other techniques must be employed, and the particular technique used must be carefully selected to work with the existing conditions; using the incorrect method can destroy latent print evidence. One common technique is the use of gaseous super glue. While the sweat in a latent print will dry after a relatively short time making dusting for fingerprints pointless, the amino acids in the print can remain for months or more given the right conditions. Super glue (all brand names are virtually identical chemically) has an affinity for these amino acids, and as such super glue gas will naturally cluster and solidify around them, leaving a sticky image of the fingerprint.
While I was in the fingerprinting
lab, I had the opportunity to view (and even
participate in) the entire process of using the super
glue technique of obtaining prints from start to
finish. The process was relatively simple. We placed
the objects that were being checked for prints in an
airtight glass chamber. Several objects are generally
treated at once. This particular time, a small
handgun, a large knife, and a drinking glass were all
placed in the chamber. The drinking glass was a
demonstration for my benefit, and had only been handled
by me and a couple of the police. Additionally, a
small test slide was placed inside the chamber. This had
been carefully and deliberately touched, and contained
a known latent print. It was used to time the gas
exposure; when the print on the slide was clearly visible,
the objects within the chamber had been exposed to the
super glue gas long enough. Lastly, a few drops of super
glue were placed in a small tin that sat on a heater
at the bottom of the chamber. The chamber was then sealed,
and the heater activated. The tiny wisps of super glue
gas that boiled away from the liquid super glue were
circulated throughout the chamber by a couple of box fans.
After roughly fifteen minutes, the print on the test
slide reached its peak of clarity and the heater and
fans were turned off.
Once the super glue gas had been completely removed from the chamber, the objects that were being tested could be removed. They were then examined, and the clearest prints on them found. These prints were dusted, and the resulting dust image of each print was lifted with a wide piece of transparent sticky tape. Each piece of tape was then attached to an index card made from frosted plastic. The card was finally labeled with pertinent information such as the original source of the latent print. The process of recording a print through the super glue method was complete.
Before I left the station, we compared the
best print from the glass with the copy of inked prints
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