"The DNA is a match."
When you hear that phrase on modern-day detective shows, you know the jig is up; the bad guy has been caught. In a fictional TV world where crimes are solved in 30 minutes, nobody ever questions the authority of DNA evidence.
In real life, though, doubt can easily be cast on it because people get confused by scientific jargon, or because of uncertainties about how the evidence was obtained and handled — in one famous case, the O.J. Simpson murder investigation, both factors ultimately contributed to the outcome of the trial.