"Deoxyribonucleic acid, or DNA, is the fundamental building block for an individual’s entire genetic makeup. DNA is a powerful tool for law enforcement investigations because each person’s DNA is different from that of every other
“Deoxyribonucleic acid, or DNA, is the fundamental building block for an individual’s entire genetic makeup. DNA is a powerful tool for law enforcement investigations because each person’s DNA is different from that of every other individual (except for identical twins). DNA can be extracted from a number of sources, such as hair, bone, teeth, saliva, and blood.”
See the full text: DNA Testing in Criminal Justice: Background, Current Law, and Grants (pdf)