Arches, Loops and Whorls Determine Your Print Category

The Babylonians pioneered their use in 1700 B.C., and societies ever since have employed fingerprints to identify criminals. Now computers and lasers are making them more valuable than ever.

Fingerprints already provide police with perhaps their most potent technical tool. Nearly 3,000 fugitives a month are apprehended through FBI fingerprint checks. It is all the result of the remarkable fact that no two humans have the same prints.

Those prints are formed by lines of pores, which secrete sweat that leaves marks on almost every surface a finger touches.

The ridges develop in apparently random patterns, and understanding their complexity has become a high science at the FBI. Examiners identify prints not by matching the ridges on fingers, but by carefully counting certain unique features.

Since skin stretches, two inked prints of the same finger can look different. So examiners look for places where ridges end or divide. These are called minutia points, and an average finger has 90 to 125. An examiner can judge whether two prints are from the same finger with as few as seven matching points.

Computers match up prints the same way, and faster. But no computer is so fast that it can match a suspect’s fingerprints against all 32 million sets of prints on file with the FBI.

So the FBI’s prints are grouped in categories that were devised in 1901 by Sir Edward Richard Henry, the British inspector general of police in Bengal, India. The groupings are based on fingerprint arches, loops and whorls. A suspect’s prints can be compared with prints in the same category.

Police are using new chemicals and lasers to better lift prints at a crime scene. In one of the most bizarre cases, a finger was recently found in the mouth of a shark caught by a fishing boat, and FBI officials were able to identify the shark’s victim.

“I have been in this field since 1957, and you can’t imagine how the ballgame has changed,” said Wendell Clements, chief of the latent fingerprint section at the Los Angeles Police Department.