Fingerprint Evidence, Evaluation of

Sources of Evidence

Impressions left by volar skin, or the ridged skin of the palmar surfaces of hands and fingers and plantar surfaces of feet and toes, play a major role in forensic science. Commonly known as fingerprints, palm prints, or footprints, recordings of this skin are often used as a form of physical evidence to link a person to a particular item or location, such as a crime scene. Perspiration, oil, blood, or other substances are often present on the skin and are deposited on surfaces such as plastic, wood, metal, or glass during touches, which might leave a recording of details of the ridge, crease, scar, and imperfection patterns from the skin. The evidence is recovered using a variety of development techniques to make the latent image, or undeveloped print, visible. These include powders, cyanoacrylate glue, chemicals, or stains that adhere to or react with the residues of the print. A variety of different lights and filters can also be used to visualize a latent print.

The basic challenge of fingerprint (more formally known as friction ridge) evidence derives from the fact that any latent print recovered from a crime scene will vary in appearance from every other latent print and from every standard print. A standard print can be obtained using a variety of techniques, from blackinked prints on a white card to electronic imaging of the volar surfaces. The intent of the standard recording is to obtain a clear set of prints from a known-source individual for comparison with the unknown-source latent prints. In some cases, these variations in appearances are trivial, and the match between an unknown latent and known inked print appears obvious. However, latent or standard prints with low quality or quantity of details are a challenge to examine, and thus the field of forensic latent print examinations uses established procedures, practices, guidelines, and methodology to support the examination of latent prints.

Friction ridge skin develops its structure in utero by means of biological, chemical, and physical processes of pattern formation known as reaction-diffusion. This process ensures that ridges form in a roughly parallel configuration and tend to orient orthogonally to lines of stress that occur during the fetal development of structures known as volar pads in fingers, palms, soles, and toes. The resulting ridges form patterns of loops, whorls, and arches in the pads of the developing finger tip (distal phalanges). Additional structure is provided by the development of ridges that form bifurcations and ridge endings, or minutiae. These minutiae are often coded when fingerprints are entered into computer databases such as the Integrated Automated Fingerprint Identification System, maintained by the U.S. Federal Bureau of Investigation.

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