A wide range of biological samples are encountered in the field of forensic science, including blood, soft tissue, semen, urine, saliva, teeth, and bone. Forensic samples are routinely found as stains on various substrates, including cotton, denim, carpet, wallboard, wood, envelopes, and cigaret butts. Prior to collection, these samples have often been exposed to severe environmental conditions, such as varying degrees of temperature and humidity, microbial and chemical contaminants, and exposure to soils and other natural substances, such as salt water.