While these are most of the principal techniques investigators use to gather clues at the crime scene, they're not the only ones. For example, if the bomber leaves a bag or backpack, an investigator might inspect it for trace elements such as pollen or pet hair. Pollen can be traced back to specific types of flowers, and forensic botanists can cross-reference these flowers against each other to determine where the bomber might have been. Pet hair can be used to determine, for example, whether the bomber owns a specific breed of dog. Once a suspect is identified, all of this evidence can be used to search his or her home for matches.