Chance Prints at Crime Scene

Inforensics,latentfingerprints are marks left at the scene of a crime which may not be immediately visible to the naked eye. To exposelatent fingerprints, technicians usefingerprintpowder, fuming and othertechniques. Identifyinglatentfingerprints is an important part of evidence collection and many technicians specialize in retrieving fingerprints from crime scenes and analyzing them in the lab in order to assistlaw enforcementwith apprehending criminals.

The hands and feet are naturally oily, due to the glands, which secrete sweat, a mixture of water, salts and other trace compounds. The sweat adheres to the friction ridges of the finger and when a finger is placed on a surface such asglass, plastic or wood, an impression known as fingerprintwill be left behind. The natural oils of the body preserve thefingerprint, which is utterly distinct; no two humans have the same fingerprints. Sometimes, latentfingerprints are made from substances other than sweat such as blood, other body fluids, or paint.

When investigators arrive at acrime scene, one of the first things they do after photographing the entire scene is dust forlatentfingerprints. Dusting for fingerprints ensures that no prints are missed, even ifpatentfingerprints, prints readily visible to the naked eye, are evident. Specializedfingerprintpowder is gently brushed over surfaces which may hold fingerprints to see if any appear. Iflatentfingerprints emerge after dusting, they are photographed and then carefully lifted withclear tape before being affixed tofingerprintcards. For difficult surfaces, another process known as fuming may be used to findlatentfingerprints. Fuming can be used for very old fingerprints, because it causes achemicalreaction with trace substances which may be left behind by afingerprint, even if the sweat itself is gone.