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Articles » Fingerprinting
Fingerprinting Questioned
Jesse Ng
Since Galton's time, fingerprinting has been used to capture and convict criminals. It has had an impeccable reputation for identifying criminals up until today. Juries relied greatly on such evidence for the acquittal or conviction of criminals. It was almost unheard of for juries to acquit a suspect if his prints matched those found at a crime scene. The practice of fingerprinting goes back to the 19th century. In 1892, Galton looked at the patterns of whorls, arches and loops that made up fingerprints. He concluded that the chance of two prints matching at random was about one in 64
billion.
However, recently, at a meeting on Science and the Law held in San Diego by America's Justice Department, a speaker hinted that the technique of fingerprinting might not deserve the credit it is given. According to the speaker, Simon Cole, the technique is "scientifically and statistically wanting." This does not mean that the world's prisons are full of innocent victims, but it is a fact that fingerprinting has never been subjected to the proper scrutiny of the scientific community. Galton's method of studying fingerprints was based on the whole fingerprint. However, in most cases, only partial fingerprints are found at a crime scene. In Galton's analysis, there was nothing that gave the likelihood of fragments of prints coinciding in different individuals. Not only are incomplete prints a problem, but also the fact that most prints found at crime scenes are what investigators call "latent." These latent prints must be treated with chemicals or illuminated with ultraviolet lights before they are visible to the naked eye. However, the question arises over how valid it is to compare "filtered" evidence to the clean prints obtained from suspects in controlled conditions.
Recently, a case has shown that Simon Cole's doubts in the fingerprinting system is valid. In 1991, Byron Mitchell was convicted of driving the getaway car in a robbery carried out in Pennsylvania. In 1998, Mitchell appealed. The case was based upon two sets of latent prints. One found on the getaway car's steering wheel and the other on the gear lever. These two sets of prints had lead to his conviction in 1991. During the course of Mitchell's trial, the FBI did something that had never been done before, which leads one to doubt the system of fingerprinting to be accurate. In the FBI's studies, the inked prints of Mitchell's fingers and the latent prints found in the car were sent to 53 state law enforcement agencies. Eight of the 35 agencies that responded were unable to find a match for one of the latent prints, while six others could not find a match for the other. This is a failure rate of 20%. There is now a serious doubt on the reliability of fingerprints. The use of a technique that has an error rate as high as 20% will inevitably raise a lot of legal questions. Until a study is performed on this technique and the true statistical value is determined, many cases will be taken before the appeals court.
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The
Economist; London; Dec 16, 2000; by Anonymous; V. 357, Issue 8201, pp. 89-90
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