When criminals commit crimes, they interact with the environment in a way that leaves behind traces of their behavior, movement, and even identity. They may flee from the scene of a crime in a vehicle that produces an impression of their tire tread in the mud, or they may leave behind a fingerprint on the sill of the window they used to gain access to a victim's home. Any time two objects come into contact with a certain amount of force, the result is an impression-sometimes visible to the naked eye, sometimes not. Impression evidence that is frequently found at crime scenes includes toolmarks, shoeprints, and tire tread marks, in addition to fingerprints and bite marks. Forensic scientists who specialize is a specific category of impression evidence are critical to its effective use in the world of criminal justice. They search crime scenes, and upon finding impression evidence, carefully document, record, and preserve it. They can also apply their extensive knowledge and training to interpret the evidence, figure out how it fits into the bigger picture, and determine whether it contains any data that can answer the who, what, when, where, why, and how of the crime.
