Fingerprint Evidence
The evidence of fingerprint rests on two basic principles:
No two people have the same pattern of friction ridges.
A person’s “friction ridge patterns” (the swirled skin on their fingertips) don’t change.
Police officers can use fingerprints to identify defendants and crime victims if a print matches one already on file. (Today, the FBI has a collection of prints that numbers in the millions.) People’s fingerprints can be on file for a variety of reasons. For example, people may be fingerprinted when they are arrested, or when they begin certain occupations. And it is increasingly popular for parents to ask local police departments or schools to fingerprint their young children, a grim reminder that children who are abducted or are the victims of other heinous crimes often cannot be identified otherwise.
How Fingerprints Are Found
Friction ridges contain rows of sweat pores, and sweat mixed with other body oils and dirt produces fingerprints on smooth surfaces. Fingerprint experts use powders and chemicals to make such prints visible. The visibility of a set of prints depends on the surface from which they’re lifted; however, with the help of computer enhancement techniques that can extrapolate a complete pattern from mere fragments, and laser technology that can read otherwise invisible markings, fingerprint experts increasingly can retrieve identifiable prints from most surfaces.
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