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Separating Fingerprint Fact From Fiction (The following paper appeared in the January 1992 issue of Law Enforcement Technology) by SHARON ALLEN The detective moved keenly through the crime scene directing his forensic people to perform various tests. The fingerprint evidence determined that the prints were made by two unidentified men and a woman. But, while “FX” may have been a great movie, it was incorrect in respect to fingerprint evidence: THERE IS NO WAY TO DETERMINE THE SEX, AGE, OR RACE OF A SUBJECT BASED ON FINGERPRINTS ALONE. A survey of prospective jurors done by Sgt. Charles Illsley of the West Utah Police Department included questions dealing with fingerprint testimony. When asked where these jurors acquired most of their knowledge about fingerprints, 58 percent listed television as their primary source, followed by newspapers, radio, books, and other sources. Frequently, crime scene technicians and lab personnel feel compelled to compete with the “Quincy's” of TV and the technology of “James Bond,” all within the time frame of “Sixty Minutes.” Although most police personnel and prosecutors are aware of the factors relating to fingerprint identifications, some myths and fallacies--—many perpetrated by the media--—still linger.
Myths and Fallacies: NO LATENT PRINTS WERE FOUND AT THE SCENE, SO HE MUST HAVE WORN GLOVES OR HE WIPED THEM OFF! There are many factors that cause an item to lack sufficient ridge detail. Surfaces, pressure, or the condition that existed before or after the finger or hand touched the surface, are some of these. If the background where the latent print is found is rough, grooved, or textured, it may impede the continuity of the ridge detail in the latent print. For example, take a plastic baggie in your hand and make a fist. Releasing the bag in your hand you will notice the baggie unraveling. The ridge detail originally connecting in its compressed state will lack this continuity in the unraveled state. The amount of pressure applied to the surface has varying effects. The results differ drastically when the items, say, papers, were “grasped or rifled” through. Again, the examiner does not always know the conditions that existed before or after the latent print touched the surface, but understanding the factors affecting latents aids the technician in explaining the fragile nature of these prints. Weather conditions may be a contributing factor in the lack of prints. In cold weather, the pores that exude perspiration tend to close. In hot weather, the opposite is true--—too much perspiration causes the recordings of the prints to be spotty and distorted. The ridges must contain some sweat, grease, oil, or other foreign matter or no latent print will be left on the item that was touched. A large percentage of latent prints are “lost” before they are received at the lab for analysis because of poor handling or packaging of items to be examined. Most crime labs readily dispense information and assistance to police who may be having difficulty or problems with evidence retrieval. THERE WERE NO FINGERPRINT IDENTIFICATIONS OF THE SUSPECT--—THERE FORE HE DIDN'T DO IT! The assumption is that if no fingerprints of the suspect were found, he is innocent. For the reasons mentioned earlier, he may not have left behind any identifiable prints linking him to the crime, but it would not necessarily eliminate him as a suspect. There may have been fragmentary ridge detail indicating the item was handled but not enough to make a comparison. In some instances, an object can be so heavily handled that the ridges overlap, preventing the examiner from determining which ridges belong to which latent print. You may also be in a position to see the item being touched in, for example, a drug investigation where there is a "hand to hand" buy. You, as the agent making the “buy,” know the subject touched the bag when it was handed to you. Yet, when the bag is processed, the results may be negative. Lack of fingerprint evidence does not assume innocence. THE EX--FRIEND OR SPOUSE'S PRINTS WERE FOUND AT THE CRIME SCENE, SO ONE OF THEM DID IT! The value of the latent print may dwindle if the person had access at one time to the crime scene. Prints can last, if they are protected, indefinitely. Because Party A stopped dating Party B, does not mean the Party B's prints will disappear from Party's A's home. Technically, the age of a latent print cannot be determined, although the age of a print may be gauged if you knew approximately when an item was cleaned. For example, if a mirror on the wall at the crime scene had been recently cleaned and latent prints of the subject were developed on the mirror, you could then ascertain that the prints were placed there sometime after the mirror was cleaned. The location where the latent print or prints were found may be significant. If a family member or friend has access to the home but that individual did not have access to a particular area or item in that home, the value of that print would be greatly enhanced. DNA “FINGERPRINTING” AND THE SCIENCE OF FINGERPRINTS ARE SIMILAR. The term “fingerprinting” used in conjunction with DNA is misleading--—DNA “typing” would be more correct. DNA is the genetic material present in every living cell, and, in theory, is unique to every individual (DNA is a new tool that can be used in conjunction with fingerprints. For more on this subject see LET, Sept. 1991, “DNA On Trial,” page 30). HERE ARE THE LATENTS FROM MY CASE! HERE ARE THE FINGERPRINT CARDS OF THE SUSPECTS! WHAT MORE DO YOU NEED? In most cases, nothing. But, many times the rolled fingerprint card may be acceptable for classification purposes, yet be of poor quality for latent print evaluation. If the latent print developed is determined to be the tip region of the finger and the rolled fingerprint card does not have the tip region recorded on the card, the examination cannot be completed. Care and effort should be taken to ascertain legible and complete fingerprints of your suspect. Although not always possible, major case prints and palm prints should be taken since a large portion of latents retrieved are from other areas of the hands, such as second joints, fingertips, and palms. WERE THE LATENT PRINTS FOUND AT THE SCENE AND THE FINGERPRINTS OF THE SUSPECT A “CLOSE” MATCH? There is no such thing as “close” in fingerprint identification. Yes, if the pattern area is visible in the latent print, a conclusion could be made to eliminate that suspect as having made that latent print--—if the latent print recovered is a loop pattern and the suspect's fingerprints have all whorl patterns. The science of fingerprints is based on no two fingerprints being alike, not even those of identical twins. Although there are three basic fingerprint patterns, it is their systematic arrangement that makes each print unique.
This article was reprinted in “THE PRINT” 10(3), March 1994, pp 5-6 |