DNA can be used to prove someone innocent or guilty.  Before any testing is done obviously a sample is needed, it could be blood, semen, hair, or skin. Everybody remembers the bloody glove and blood in the bronco that was tested in the O.J. Simpson trial. Technology can match blood samples, find a suspect, or even find out who the father is. This form of identification is much more accurate then fingerprints, but it takes longer and it's more expensive to perform. The DNA sample from the scene of the crime is matched with the DNA from the suspect. If they match it is the same DNA and the suspect is guilty (or innocent).