forensic science involves using scientific techniques in a criminal investigation and trial. physical evidence refers to guns, knives, bloody shirts, or even documents found at a crime scene. trace evidence refers to very small pieces of evidence like strand s of hair, skin cells, or finger prints. temperature is on important indicator telling investigators when a person died, usually called "time of death." another factor forensic investigators look for on a dead body is rigor mortis. a few hours after a person dies, the joints of a dead body stiffen and become locked in place.