But a six-month investigation by 60 Minutes and The Washington Post shows that there are hundreds of defendants imprisoned around the country who were convicted with the help of a now discredited forensic tool, and that the FBI never notified them, their lawyers, or the courts, that the their cases may have been affected by faulty testimony.
The science, called bullet lead analysis, was used by the FBI for 40 years in thousands of cases, and some of the people it helped put in jail may be innocent.
For years, the FBI believed that lead in bullets had unique chemical signatures, and that by breaking them down and analyzing them, it was possible to match bullets, not only to a single batch of ammunition coming out of a factory, but to a single box of bullets.
The Quantico lab was the only place in the country that did bullet lead analysis, and the assertion that you could actually match a bullet fragment to a specific batch or box of bullets went unchallenged for 40 years -- until William Tobin, a former chief metallurgist for the FBI retired in 1998 and decided to do his own study, discovering that the basic premise had never actually been scientifically tested.
Asked what he found out, Tobin tells Kroft, "It hadn't been based on science at all, but rather had been based on subjective belief for over four decades."
"So what you're saying is that this is junk science?" Kroft asks.
"That's correct," Tobin says. "It's worthless as a forensic tool."