Crime Science: Methods of Forensic Detection by Joe Nickell & John F. Fischer

Author:Joe Nickell & John F. Fischer [Nickell, Joe & Fischer, John F.]
Language: eng
Format: epub
Tags: law, Criminal Procedure, Forensic Science, Social Science, Criminology, True Crime, Forensics
ISBN: 9780813120911
Google: OMMEAQAAIAAJ
Publisher: University Press of Kentucky
Published: 1999-11-15T00:11:19.015532+00:00

SHOE AND TIRE IMPRESSIONS

Shoe prints and tire prints are left in much the same way as are fabric and other types of impressions. The shoe or tire becomes contaminated with some substance such as blood, oil, or dust, and a latent or visible print is left; alternatively, the print may be a plastic or three-dimensional one, pressed into mud, for example.

Latent shoe prints are searched for and developed in much the same way as glove and other fabric prints. Whenever the impression is made by dust or other powdered material, the procedure is first to photograph it—oblique lighting is usually helpful—and then to lift it in the manner suggested for fabric prints; that is, by using sheets of lifting material or by the electrostatic technique. Comparison footprints may be made by coating the soles with water-based ink applied from a large ink pad; the shoes are then stepped onto an acetate sheet or a sheet of tracing paper.8 When the contaminating substance is blood—as in the case of a completely invisible shoe print left at the scene of a double homicide in Nome, Alaska—it may be developed by spraying with the chemical reagent luminal. The result is a faintly glowing print that must be observed in darkness. In the Nome case, the developed and photographed print was successfully matched with a test impression made from the shoe of the suspect.9

When either a shoe or tire impression has been left in some moldable substance such as clay or snow, it is first photographed from directly above to avoid distortion, and then it is cast. Traditionally, plaster of paris has been used to cast shoe and tire impressions, but in recent times dental stone has been found superior. In either case, because the weight of the soupy material may damage or distort the impression, the surface is first carefully sprayed with shellac or clear acrylic lacquer. With imprints in snow, a special Snow Print Wax is used instead. Two coats of the proper preservative are applied, with sufficient drying time allowed between applications. Next, a retaining frame with a depth of two inches is placed around the impression, and the casting material is carefully poured in. (In the case of plaster of paris, the cast is reinforced by placing wire mesh over the print after the pouring reaches a depth of about half an inch, followed by the deposit of the remaining one and one-half inches of poured plaster.) Before the plaster or dental stone has hardened, identifying information is scratched into the surface.10

If the impression is clear, examination of the recovered shoe print or tire print may permit determination of the manufacturer of the shoe or tire from the class characteristics.11 The FBI maintains a vast file of both shoe (sole and heel) patterns and tire-tread designs for such identifications.12 For example, during the murder trial of O.J. Simpson, the prosecution introduced evidence identifying bloody shoe prints at the crime scene as having been made by size-twelve Bruno Magli shoes—designer footwear that is both expensive and rare.

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