The matching of fingerprints requires good eyesight and intense concentration.
The process is similar to one of those puzzles where you have to spot the differences between two apparently identical pictures. With fingerprint identification, the reverse applies – the fingerprint expert has to look for the similarities.
Fingerprints are normally stored by name on card-index systems at a control fingerprint bureau. In most countries, only the prints of convicted criminals together with unidentified marks in unsolved cases are kept.
Some countries keep a national archive of fingerprints but because of the time it can take to search, it is usually considered as only a back-up, for use if a mark is not matched locally.
Files of criminals with known specialties, such as car thieves or handbag snatchers, are also kept. Secret police forces and intelligence organizations also keep their own files of people they consider to be revolutionaries or enemy agents.
A fingerprint officer will begin by examining the marks taken from the scene and memorising their characteristics. He will then compare them against prints taken from innocent people who might have left marks at the scene – members of the family or policemen, for example. Any marks that match the innocent prints are rejected. The fingerprint officer then takes from the file all prints of possible suspects, whose names have been supplied by the investigating detective.
If these do not match, the officer has to make a wider and more painstaking search. If he is searching for a burglar, he will begin looking through all burglary cases in the locality and then all those from the adjoining town or area.
Depending on how much time was ordered to be spent on the search, he might pursue it through neighboring fingerprint bureaus in other police forces. The search for a house burglar can be widened to other potential types of criminals, such as safe-crackers, but the officer might not feel it worthwhile to extend the search to criminals who only pass bogus cheques.
Fingerprint officers also check the fingerprints of newly arrested criminals against unidentified marks from other crimes in the hope of clearing up unsolved cases. They will also compare unidentified marks against new marks to see if a series of crimes can be established. Officers can make dozens of comparisons a day, but many work for days without ever having a positive identification.
Most of this work is manual and can be very laborious. In the early 1980s electronic systems were developed to speed up the work. Prints and marks can now be stored and retrieved on electronic indexing systems, so that the press of a button calls up all the prints of, say, known car thieves living in a certain area and aged under 30. Systems can now be linked up between neighbouring forces, or with national collections, to widen the potential search. However, the actual comparison still has to be carried out by the fingerprint officer.
Scientists around the world are developing computer systems which store, retrieve and, most importantly, match prints and marks. Some matching methods, which can make 60,000 comparisons a second, are already being used by local police forces. But a fully automated, national fingerprint system is still in the future.
Picture Credit : Google