DNA is contained in blood, semen, skin cells, tissue, organs, muscle, brain cells, bone, teeth, hair, saliva, mucus, perspiration, fingernails, and urine. DNA is similar to fingerprint analysis in how matches are determined. When using either DNA or a fingerprint to identify a suspect, the evidence collected from the crime scene is compared with the “known” print. If even one feature of the DNA or fingerprint is different, it is determined not to have come from that suspect. Forensically, valuable DNA can be found on evidence that is decades old. Several factors can affect the DNA left at a crime scene, including environmental factors. Not all DNA evidence will result in a usable DNA profile. DNA evidence can be collected from virtually anywhere. Only a few cells can be sufficient to obtain useful DNA information. Investigators and laboratory personnel should work together to determine the most probative pieces of evidence and to establish priorities. Every officer should be aware of important issues involved in the identification, collection, transportation, and storage of DNA evidence. Biological material may contain hazardous pathogens such as the HIV virus and the hepatitis B virus. Because extremely small samples of DNA can be used as evidence, greater attention to contamination issues is necessary when identifying, collecting, and preserving DNA evidence. When transporting and storing evidence that may contain DNA, it is important to keep the evidence dry and at room temperature. As with fingerprints, the effective use of DNA may require the collection and analysis of elimination samples. CODIS (Combined DNA Index Systems), an electronic database of DNA profiles that can identify suspects, is similar to the Automated Fingerprint Identification System where suspects can be identified or linked to a crime scene through search analysis.