The process of linking physical evidence to a common source. Individualization is a process that starts with identification, progresses through classification, and leads, if possible, to assigning a unique source for a given piece of physical evidence. The term individualization is often mistaken for identification, which in the forensic context does not have the same meaning. In forensic science, to identify something means exactly that to determine that a red stain is blood or that a white powder is cocaine. However, a statement such as The fingerprint was identified as belonging to John Doe is incorrect in the strict sense. Rather, the fingerprint has been individualized and linked to John Doe as the one and only possible source. The idea of a common source comes in when one considers how such a fingerprint might be used. If John Doe left a fingerprint on a gun, that latent print could be developed and subjected to a database search, which would, in this example, lead to the identification of several people whose prints were in the database and who might have contributed the print. A fingerprint examiner would compare the print found on the gun to the prints on record and determine that the evidence print matched that of Mr. Doe. The two prints, the one on the gun and the one in the database, have a common source John Doe. The print on the gun is thus individualized.
Aside from fingerprints, the other kinds of evidence that can potentially be individualized in a similar manner are blood (via DNA typing) and impression evidence, such as markings made on bullets and toolmarks. Less obvious but extremely important in forensic analysis is individualization by way of a physical match. It is not that the evidence itself is unique but rather the way in which it was separated and pieced back together that allows for linkage to a common source. As an example, consider a case in which a body is wrapped in a torn white sheet. The sheet is recovered and preserved, ragged torn edges intact. Meanwhile, a suspect is developed and a search of her house leads to the discovery of a portion of a white sheet. If the torn edges of the burial sheet and the sheet found at the house match, that is an example of a physical match, which leaves no doubt that the two pieces were once part of the same whole. Sheets themselves are not chemically or physically unique in the same sense that blood or fingerprints are, but the random tearing pattern is.