Amurder victim is found in their apartment with a gunshot wound to the chest. the lock on the door has been forced open by some kind of wrench or crowbar. there are distinct footprints in the victim's blood that has pooled on the floor. on the desk, investigators see two opened soda cans. the victim's computer is open to the email program, with an unsent message. what evidence in this crime scene could possibly be tested for dna to identify the perpetrator?