It may not be immediately apparent how daring that inquiry was 22 years ago. DNA testing was then in its early days as a tool in criminal justice, and few people anticipated that prisoners would clamor to have old biological evidence retested in hopes of clearing their names.

Moreover, hardly anyone was willing to say aloud that innocent people really were locked up. Politicians could not spend money fast enough on prisons. After a long climb in crime rates, the country was ratcheting up sentences. Bill Clinton had suspended his presidential campaign in 1992 so that he could be in Arkansas, where he was then the Democratic governor, for the execution of a murderer who had shot himself in the head and was so brain-damaged that he asked prison guards to save the pecan pie from his last meal for him as he was being led to his lethal injection.

Ms. Reno had read, though, about the exoneration of 16 people, including a former marine, Kirk Bloodsworth, who had been sent to death row in Maryland for the killing of a child on the strength of testimony by five eyewitnesses.

At such a tough-on-crime moment, the notion that fallibility was poured into the foundation of the criminal justice system was startling and disruptive. Ms. Reno, who died this week at 78, was unafraid of looking directly at it. The first woman to hold the position of attorney general, she served eight years.