Jobs You Don't See on CSI #4: Forensic Dachtyloscopy

by Russ Stover
Don't let television fool you-criminal justice, criminology, and forensics are far more than medical examiners, chases, and millions in lab equipment. There are many jobs done every day by hardworking people that do not make it off the cutting room floor. This edition we will be talking about forensic dachtyloscopy or as its more commonly known: fingerprints.

Fingerprints are one of the oldest weapons in the investigator's arsenal. A fingerprint is the impression left by the ridges on human fingers, palms, even feet. Ridges are the raised parts of the skin that aid in gripping. Impressions can be left on many different kinds of surfaces like metal, wood, plastic, leather, etc. The leaving of these impressions is helped by the natural and applied oils and sweat of the body.
Fingerprint identification is done by comparison of two impressions to find if they are from the same person. The nature of skin means that no two fingerprints are exactly the same but there are certain parts of the prints that never change. It takes an expert or a computer system to determine whether they are the same (ident) or not the same (nonident). When creating a fingerprint file the fingers are either rolled in black ink then rolled onto a card or created digitally with a live scan. A latent print is the random impressions left on walls or doors that can only be found by powders or ultraviolet light.
Types of Fingerprints
Exemplar prints are prints taken from a known subject like when a person is arrested, applies for a government job, or joins the military. These prints are scanned and added to the FBI's database for use in criminal investigations, the identification of unknown persons like John Does, or bodies in accidents.
Latent prints are the invisible prints left by ridges on some kind of surface. Some latent prints may be full impressions while others, called partials, are parts of a full print. Latent prints can be difficult to judge in comparisons.
Plastic prints are the ones that are obvious to the eye without the use of powders and dyes or lights.
Classifications of Fingerprints
Modern fingerprint classification owes a lot to the Henry Classification System. The Henry system was developed in India and adopted in Britain. There are three types: the loop, arch, and whorl. Most prints are loops with differing numbers of loops, length, and are either radial or ulnar depending on whether they turn toward the radius or ulna bones of the arm. Whorls look like targets and include plain, double loop, composite, peacock's eye, accidental, and central pocket. Arches look like, well like arches. Prints also have what are called bifurcations and deltas. Bifurcations are splits in the ridges like the branching of trees and deltas look like the deltas of rivers with branches coming off of branches in a small spot. The number of ridges between bifurcations and the center of a loop or the number between the center of a whorl and a delta can help identify someone. Then there are many odd bumps, splits, cracks, and shapes in fingerprints. I have seen targets, letters, even one of my own prints looks like a cyclops.
The modern system uses a system of five fractions with R for right and L for left, i for index finger, m for middle, t for thumb, r for ring, and p for pinky. Then each is numbered depending on whether or not it is a whorl. The first whorl is a 16, the second an 8, and so on. Arches and loops are 0s. They are all added up and the two hands divided to give a single number. That number then reduces the total of prints needed for comparison.
In the 1990s researchers found that the impressions left by children's fingers disappear faster than adults. This is due to having less oil on their bodies than adults. Fingerprints can also leave behind the chemicals in the body. These can be found and checked for drugs, tobacco, coffee, etc.
The FBI maintains the world's largest database called the Integrated Automated Fingerprint Identification System or IAFIS with over 51,000,000 criminal and 1,5,000,000 civil records. Unlike what you may have seen on television the FBI strives for a two hour turnaround time for criminal files and 24 hours for civil and while they often come through they are not nearly as fast as on CSI. Also, dusting a crime scene for prints is tedious work that can take considerable time and patience. So the next time you see Horatio wanting lab results back, think about some poor soul at a nondescript building in cold, gray West Virginia sitting in front of a computer comparing prints and you will be far closer to the truth.
Pay: FBI Fingerprint Examiners make about $30,000 or more per year. Those of local and state agencies make about the same. There are some latent jobs in the defense and intelligence industries that make as much as $100,000.
Training: the FBI has a top notch training program that lasts three months or more but is only open to law enforcement. There are universities and private training available with certifications as well.
*By the way, if anyone noticed those are Elvis' prints at the top, well done.

Further reading:

The Science of Fingerprints Classification and Uses-Federal Bureau of Investigation.

Beavan, Colin. 2001. Fingerprints: The Origins of Crime Detection and the Murder Case that Launched Forensic Science. New York: Hyperion.
Advances in Fingeprint Technology-R.E. Gaensslen (ed.)
Fingerprints online:

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