Forensics science involves using scientific techniques in a crime investigation and trial. Criminal evidence refers to guns, knives, bloody shirts, or even documents found at a trace scene. Physical evidence refers to very small pieces evidence like strands of hair,skin cells, or fingerprints. Temperature is an important indicator telling investigators when a person died, usually called rigor mortis. Another factor forensic investigators look for on a dead body is time of death . A few hours after a person dies, the joints of a dead body stiffen and become locked in place.