Friday, March 27, 2009

Class v. Individual Characteristics

Within forensic science, there are two types of characteristics, class and individual. These are forms of physical evidence that become crucial to solving a crime. With the use of new technology, the scientists are able to determine if a known sample of a small fiber, paint chip, or shoe pattern is consistent with the unknown sample found at the scene. When individual characteristics are determined, the suspect has been linked to the scene.

Physical evidence establishes that a crime has been committed, establishes the key elements of the crime, links the scene to the victim, the victim to the suspect, and the suspect to the scene. Besides DNA, the next best evidence would be individual characteristics. But first, the evidence must be classified with class characteristics, which is more general.

Class characteristics are general characteristics that define a category of items or objects, but are not alone sufficient to define individuality. An example would be a shoe print in the dirt. The print is lifted for comparison. There are hundreds of different shoes in the world, with hundreds of different sole patterns. Class characteristics allow the scientists to narrow the pattern down to specific shoes. The FBI has created a shoe and tire database for such purposes. Once the laboratory has narrowed the pattern to one shoe pattern, they are able to address the issue of whether or not it was the print found at the crime scene.

Individual characteristics are exceptional characteristics that may establish the uniqueness of an object. These unique markings are accidental, or unintentional, characteristics resulting of wear and random markings on the item during manufacturing. The way in which a person walks creates a wear pattern that is unique only to them on the soles of their shoes, along with normal wear of the shoes. This is what the scientists look for when doing a comparison. Scientists are matching up the individual characteristics of the known sample (suspect’s shoe) and unknown sample (print at the crime scene).

With such evidence, the scientists are able to state that the suspect’s shoe was without a doubt, the shoe that was found at the crime scene. This places the suspect at the scene, which is what is needed to prove that the suspect could have committed the crime. Class and individual characteristics can also be found in fingerprints, on a spent bullet, a prying tool, and tread patterns of an automobile.

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