In the 1990s DNA fingerprinting, or the identification of an individual through a sample of his or her DNA, became an indispensable tool in investigations of murder, rape, and other crimes where the offender might leave at the scene a trail of physical evidence in the form of, hair, skin, or bodily fluids. In 1998 the Federal Bureau of Investigation (FBI) opened a national DNA database of people convicted of certain serious offenses. DNA testing was also used in some cases to prove the innocence of convicted prisoners. A group called the Innocence Project sought DNA testing for convicted rapists and murderers, and by 1999, at least sixty-one inmates had been exonerated. DNA fingerprinting had other uses as well. In 1992 the U.S. Army began collecting blood and tissue samples from all new recruits as part of a "genetic dog tag" system, aimed at better identifying...