Besides blazing new paths in health science, genetics is transforming the way in which criminal investigations and trials are conducted. The importance of DNA evidence rests on a single but crucial fact: Every individual's DNA is unique (except in the case of identical twins, who have identical genomes). A person's DNA profile can be used like a fingerprint to link suspects to crime scenes and victims. DNA profiling-also called DNA fingerprinting or DNA typing-has been responsible for overturning verdicts and saving innocent people from execution. The process is complicated and controversial. Nevertheless, it has earned itself a place in police probes and courtroom proceedings, and the science behind it is compelling enough that it is likely to play a major role in the future.

The Battle over DNA

Proponents of DNA analysis had to fight against strenuous opposition before the judicial system...