With the exception of identical twins all humans havea unique set of DNA that is presented in their hair, skin, blood and other body fluids. Because of this genetic fingerprint, forensic testing has become an invaluable source of physical evidence for law enforcement in obtaining convictions and in exonerating the wrongly accused. In 1985, Professor Alec Jeffreys of the University of Leicester discovered that each person carried a genetic fingerprint in his or her DNA. This discovery was first put to the test in an immigration case; a year later, DNA profiling was used in a criminal case---a double homicide in England---and helped prove the innocence of a man who gave police a false confession. The DNA obtained from crime scenes in 1983 and 1986 proved that the same man raped and killed the two young girls. With the killer's DNA on file and new crime fighting technology at their disposal, police collected blood samples from more than 5,000 men in the community. The killer was eventually caught. In the United States, in 1987, a rapist in Florida was the first person to be convicted through the use of DNA evidence.