![]() Nothing, not even Galton's original analysis, has anything to say about the likelihood of fragments of prints coinciding in different individuals. What are being compared are thus not whole prints, but mere fragments. The first is that fingerprints found at crime scenes tend to be incomplete. ![]() And two other things make the situation worse in practice. ![]() That puts fingerprinting on shaky theoretical ground. Nor has the alternative technique, recently introduced in England, of relying on an examiner's overall impression of a match, without any attempt at quantification. Unfortunately, the validity of this process, and the number of points of similarity needed to make it statistically secure, have not been scientifically investigated. Current practice, which varies widely from one place to another, has been to declare a match if there are somewhere between eight and 16 points of similarity linking a print found at a crime scene and one taken from a suspect. Galton's estimate relied on using every available point (there are generally between 35 and 50). These are now known as “points of similarity”, or “Galton details”, and if two prints have enough points in common they are deemed to be identical. Instead, he identified places where the ridges of which fingerprints are composed either end or split. Besides, Galton was not really comparing whole prints. That estimate, however, has never been backed up by any data. In 1892 Galton looked at the pattern of whorls, arches and loops that make up fingerprints, and estimated that the chance of two prints matching at random was about one in 64 billion. Modern fingerprinting goes back to Francis Galton, a 19th-century British scientist who, ironically, helped to pioneer the use of statistics. But the fact is, according to Dr Cole, who researched the subject at Cornell University, that fingerprinting has never been subjected to the scientific scrutiny required in a modern courtroom. Galton forensic science full#This is not to say that the world's prisons are full of innocent victims of dodgy evidence. And, surprisingly, he has found it is scientifically and statistically wanting. For he is one of a small group of people that has started looking at the technique which, above all others, gave forensic “science” its scientific status. Understandable, but not, says the speaker, Simon Cole, justified. What jury would acquit a suspect if his prints matched those found at the scene of a crime? It was thus understandable that when a speaker at a recent meeting on Science and the Law held in San Diego by America's Justice Department hinted that the technique might not deserve its aura of infallibility, an FBI agent in the audience took voluble issue and was later overheard calling him an unprintable name. ![]() FOR most of the century since it made its courtroom debut, fingerprinting has enjoyed an impeccable reputation for identifying criminals. ![]()
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