Sunday, June 27, 2010

Impression Evidence

This type of evidence is created when one object is pressed against another material such as soil with enough force that an impression is made of the object. Although soil is used as an example here, any material that can be manipulated with force may contain impression evidence. Other such materials may be wet cement or tar, wood, snow and even metal. Most only think of shoes and tires when considering impression evidence, but tools and bullets can also cause impressions.

Shoe impressions can provide a great deal of information for investigators about the offender. First, a shoe impression can allow the identification of the type of shoe worn by the offender, although this may only be considered class evidence if there is not any defects or wear that might allow for individualization of the specific shoe. Individual wear patterns on a shoe can be caused by the way a person walks or if the shoe is used in an area such as on gravel or hot tar that causes unique defects. If a specific shoe can be identified and linked to a suspect, this can be used to prove that the suspect was at the crime scene. If there is a series of crimes where shoe impressions were found, this can be used to link the cases as being committed by the same offender. Several different shoe impressions at a crime scene can assist in identifying more than one offender responsible for a crime. Depending upon the condition of the soil and when the crime scene is found, it may be possible to use shoe impressions to estimate the size of the offender by measuring the depth of the impression as compared to a known sample.

Tire impressions can be used to identify the type of tire on the offender's vehicle by comparing the impression against a database of known treads by manufacturer. Like shoes, tires provide class evidence unless individual characteristics can be determined. Individual characteristics can be caused by defects and uneven wear on the tire that would identify it as a specific tire related to the crime. Causes for defects and uneven wear on a tire can be caused by nails, gravel, past attempts to patch the tire, and by unbalanced tires or from frequent sudden stops that result in skidding.

Tools create marks when they come into contact with materials with sufficient force. Wire cutters, bolt cutters, screwdrivers, and crow bars are often used to pry open windows and doors and will leave evidence where they came into contact with materials.

No comments:

Post a Comment