How Are Fingerprints Lifted at a Crime Scene?

Written by collin fitzsimmons
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How Are Fingerprints Lifted at a Crime Scene?
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Fingerprints are defined as the highly individualised pattern of ridges and valleys on the skin on the fingers, and are commonly used for identification in criminal proceedings. They are highly useful because they can be left behind inadvertently, and thus link disparate elements to understand a crime scene. The method chosen to lift the fingerprints from the crime scene depends on the fingerprint and the situation--there are more than 100 different ways to capture fingerprints, although fewer than 20 are routinely used in criminal proceedings. However, even once a fingerprint is captured, there are considerations: because the skin on the fingers flexes and moulds, all fingerprints are unique from each other at least slightly, including consecutively acquired standardised fingerprints..

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Fingerprints and Identification

Fingerprints are defined as the highly individualised pattern of ridges and valleys on the skin on the fingers, and are commonly used for identification in criminal proceedings. They are highly useful because they can be left behind inadvertently, and thus link disparate elements to understand a crime scene. The method chosen to lift the fingerprints from the crime scene depends on the fingerprint and the situation--there are more than 100 different ways to capture fingerprints, although fewer than 20 are routinely used in criminal proceedings. However, even once a fingerprint is captured, there are considerations: because the skin on the fingers flexes and moulds, all fingerprints are unique from each other at least slightly, including consecutively acquired standardised fingerprints..

Types of Fingerprints

The type of procedure used to capture the latent print depends on the type of fingerprint. Most fingerprints are latent prints, meaning an accidental impression that may or may not be visible by the naked eye. Latent print residue includes sweat from the hands, mostly water and salts, as well as sweat from the face and head and other contaminants (blood, paint, ink, dirt). Patent prints are obvious to the human eye and are caused by leaving finger deposits such as ink or blood on a surface. Patent prints are typically photographed for identification, not 'lifted' like latent prints.

Lifting Latent Prints

Fingerprint detection is complex--there is no one set way that criminal investigators lift prints, and the decision on proper methodology for lifting is a highly technical skill. It is typically necessary to use a "developer," such as a chemical reagent or special powder, to achieve contrast between the ridge patterns and the surface to enable identification. This chemical is often applied with special fingerprint brushes, made of natural hair, feathers, or fibreglass. Developing agents are diverse and depend on the presence of organic materials or salts (or actual sweat, although in less than 24 hours the aqueous secretions evaporate, leaving only salts and other refuse behind). The type of chemical depends largely on the placement of the fingerprint - if the fingerprint is on a light surface, darker chemicals will be used, whereas if the fingerprint is on a dark surface bi-chromatic power is popular (which includes a mixture of black and a light colour powder, like white or silver). If chemicals are not applied at the crime scene, specialist laboratories might be enlisted, which can use high-powered fingerprint techniques. Some of these advanced techniques can detect fat layers as thin as one molecule.

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