If biological material is deposited on an item during the commission of a crime a DNA profile may be obtained from evidence collected during the investigation. DNA testing may be requested for a variety of cases ranging from vandalism to homicide. Virtually any item may, depending on the situation of each unique case, be a potential source for DNA. In some cases DNA may be obtained from a visible stain of a body fluid like blood or saliva. In other cases an item may be processed in the hope of obtaining DNA from the sloughed skin cells of the wearer of an item of clothing or the handler of a tool. Many items will be swabbed to remove DNA from their surface; a piece of soft items, like clothing or upholstery fabric, may be cut off and processed directly during DNA testing.
A DNA profile obtained at the VFL provides investigative information only by comparing it to one or more known DNA profiles. The locations tested (STRs) do not provide information about the physical features, age, or ancestry of the person who deposited the DNA. Rather, they provide a string of numbers that can be compared between samples to provide associations. Unknown profiles from evidence can be compared to DNA standards (generally cheek, or buccal, swabs) from individuals thought to be connected to the case, such as victims, suspects, or other persons of interest. Alternatively, eligible unknown evidentiary profiles can be compared to evidentiary profiles from other cases and to convicted offender profiles using CODIS.