About Fingerprints
Fingerprints are the stuff of whodunit mysteries, crime shows and real life forensic work. It is well-known that no two fingerprints are the same. The science of fingerprints is now more than 100 years old, and was one of the first means of making a positive identification of a criminal based only on trace evidence left at the scene, and a categorization method developed by a British police commissioner in India, the Henry System, is still in use today.
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Identification
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Fingerprints are an impression when the raised ridges on the skin of the bottom of the last joint the fingers and thumb comes into contact with a surface. As each person's finger prints are unique, the taking of fingerprints provides a certain means of identification. It should be noted that while comprehensive scarring might do sufficient damage to eliminate the old ridge pattern on the fingertips, it replaces it with a new and equally unique pattern.
Taking Fingerprints
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In the sort of identification processing used in a government job application or when placed under arrest, recording fingerprints is easy: the fingers are inked and then rolled onto a form to record the fingerprint image. Lifting fingerprints from a crime scene is more involved. Fingerprints on surfaces can be either latent or patent. Latent fingerprints are what happens when substances, like skin oil or sweat, are left behind on an object through direct fingertip contact. Because of the substances involved, these are rarely visible to the naked eye. Making them visible means using a "developer," typically a powder or chemical reagent, to intensify the contrast between the ridges and valleys in the image. The use of powders to do this has given rise to the expression "dusting for fingerprints," which is often put to general use on crime shows, even though not all latent fingerprints are "dusted."
By contrast, patent fingerprints are left behind because either the finger or the object's surface is smeared with a more visible substance, such as ink. The result is a clear image. Patent fingerprints should be thought of as being similar to the deliberate ink fingerprinting done when a person is placed under arrest in terms of clarity: while they may be smudged or partial, at least the stand out. Latent prints do not.
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The Henry Classification System
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The system for identifying and cataloging fingerprints used in the English-speaking world is the Henry Classification System. According to this system, there are three basic patterns in finger prints: the arch, the loop, and the whorl. Loops can be radial or ulnar, depending on which side of the hand the loop's tail points towards. Whorls are divided into accidental whorls, double loop whorls, central pocket loop whorls and plain whorls.
This system categorizes fingerprints into types. By categorizing them, the time and effort spent looking for a match is reduced. This was an important consideration in the days before computers and digital records, when up to hundreds of thousands of fingerprints could be on file at a major police department, and all searching and matching would have to be done by hand. It still remains useful for computerized searches. Once the vast bulk of fingerprints on file are excluded for not being in the same category, a more detailed examination of individual fingerprints can begin. The Henry System is the basis for the Automated Fingerprint Identification System.
Reliability
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Although fingerprints have come under some criticism for being unreliable and unscientific, they remain a core element in forensic science. There have been some well-publicized errors involving fingerprinting, the most recent being that of Brandon Mayfield, who was identified on the basis of fingerprints as being connected to the 2006 Madrid Bombing, and was arrested in the US. Mayfield, a convert to Islam with an Egyptian wife, had nothing to do with the bombing and was identified incorrectly due to incompetence at the FBI. That is the common thread of all incorrect fingerprint matches: human error. After being in use for more than a century, and with billions of fingerprint records having been taken, no two have ever been found to be identical, so the scientific basis for fingerprinting remains sound.
Fingerprints vs. DNA
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The advent of DNA identification technology forces forensic investigators to make a pretty quick decision at a crime scene: do they want fingerprints or DNA? Swabbing a fingerprint in an attempt to collect DNA material from it will destroy a finger print; use of a fingerprint developer will destroy the DNA. There are new and experimental technologies for lifting fingerprints without applying DNA-destroying developers, but they are not widespread and not fully tested.
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Comments
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fantastic!
