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The various law enforcement agencies around the world, such as the FBI and the Metropolitan Police in London (UK) have over the years built up vast collections of fingerprints.

When a fingerprint has been found at a scene of a crime it is first classified. On the basis of this classification a "short list" of similar fingerprints from the files are compared with the print from the crime scene to try and establish a match, and therefore a identify a possible suspect.

This process used to be done laboriously by hand, but since the introduction of computer technology it has been possible to automate this process using automated fingerprint identification systems (AFIS). A schematic of an AFIS is shown below;

A photograph of the print from the crime scene is scanned into a computer using  image digitising software. Using sophisticated software the image of the fingerprint is compared with the computerised database of prints and a list of possible "hits" is produced. It is then up to the fingerprint expert to make the final decision as to whether there is match or not.

This approach has revolutionised criminal investigative used of fingerprints. A computer can make thousands of comparisons in a second, thus increasing the chances of finding a match in a far shorter time than was previously possible. Shortly after being brought on-line for the first time in 1985 the Los Angeles Police Department's AFIS helped bring to justice the multiple killer known as the Nightstalker.

Case History:  The Nightstalker

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