Fingerprints are powerful investigative and prosecutorial tools because no two people have the same ones, not even identical twins or other multiple siblings who share the same DNA.

But before the Automated Fingerprint Identification System came into common use less than two decades ago, latent fingerprints -- those found at crime scenes -- usually were useless unless a police officer could give a fingerprint examiner the names of potential suspects. Narrowing the field for the examiner was necessary because it was not possible to compare latents with all fingerprints of known people on file.

With a limited number of possibilities, an examiner would compare filed prints with those from a crime scene. If no match was found, police would have to develop additional suspects for further comparison.

But with AFIS, the impossible is now possible -- and in minutes. The system speeds through millions of stored fingerprints to find "candidates" whose stored prints at least have some similarities in the arcs, whorls, loops and other identifying characteristics to those of latent prints scanned into the system.

A fingerprint examiner then compares the filed prints of the candidates, often numbering 18 to 24 people, to determine if they match the crime scene prints.

But AFIS's speed has created more work for fingerprint examiners. Because police agencies no longer need the names of potential suspects to submit latent prints for comparison, they are submitting prints from many more crimes than ever before.

Each latent print requires an examiner to prepare it for AFIS's search by scanning it into the system, "editing" a geometric pattern the computer system creates of perceived points of possible comparison, and then comparing the latent prints with those of candidates provided by AFIS.