Mr. Williams’s case highlights gaps in the body of legislation that has been passed to protect against wrongful convictions, particularly as DNA science grows more sophisticated. In all 50 states, those who have been convicted can, with a judge’s permission, run DNA evidence through a national database, sometimes yielding a hit on someone else. The same is not true of the national fingerprint database.

Mr. Williams first requested that the fingerprints be run against the national database in 1999, but prosecutors opposed the move and there was no statute entitling him to do so. About four out of five exonerations are achieved without DNA evidence, according to the National Registry of Exonerations. Yet only a handful of states allow post-conviction access to the fingerprint database, much less account for emerging technologies such as facial recognition.

“It was incredibly frustrating to know that there was technology out there that would lead to the truth, that would give him his innocence — and we were blocked from it,” said Vanessa Potkin, a lawyer with the Innocence Project, a nonprofit organization that assisted Mr. Williams with his exoneration.

As the wave of exonerations continues, more attention has been placed on the severe consequences of letting the real perpetrator go free. The man now believed to have committed the Baton Rouge rape that landed Mr. Williams in prison, Stephen Forbes, died in prison in 1996. He had gone on to commit at least five more rapes, according to his own confessions.

There has been no comprehensive accounting of the number of such crimes. But one woman, Jennifer Thompson, who misidentified the perpetrator of a sexual assault against her and wrote a book with the man who was wrongfully convicted, was later approached by another woman who had been assaulted by the real perpetrator.