Even tiny things can be the clinching evidence of innocence or guilt.

Imagine that you are a police detective sitting in a courtroom during a trial. The man accused of being a car thief says he is innocent and claims that the police have made a terrible mistake. There is no doubt in your mind that this person committed the crime. Next to testify is a scientist from the crime lab. The scientist shows the court two DNA fingerprints. The first came from a hair sample found in the stolen car.