A Florida man who served more than 34 years of a 400-year sentence for an armed robbery conviction was released Wednesday after prosecutors discovered he was likely misidentified.

The release of 57-year-old Sidney Holmes comes less than a week after a New York man, Sheldon Thomas, was freed after 18 years following a wrongful murder conviction.

The week before Thomas’ release, Maurice Hastings was declared innocent in California after nearly 40 years in prison.

All three men were exonerated after conviction review units in local prosecutors’ offices reinvestigated their cases. These units, also called conviction integrity units, have grown exponentially in recent years and experts say their impact could stretch beyond freeing the wrongfully incarcerated.

“A CIU both looks back to identify cases in the past that need to be revisited,” said Marissa Bluestine, assistant director of the Quattrone Center for the Fair Administration of Justice at the University of Pennsylvania Law School. “But it’s also learning from that error to prevent those errors from happening in the future.”

What are conviction review units?

Conviction review units conduct extrajudicial investigations into past convictions to determine if they should be vacated because the person who was convicted is innocent or because the process of convicting them was flawed, said Bluestine, who ran the Pennsylvania Innocence Project for a decade.

She said some units also conduct audits of cases involving bad actors and issue case corrections, where prosecutors determine a person was convicted of a more serious crime than they should have been and adjust sentencing.

Some units have multiple attorneys, investigators and support staff. However, others are essentially “one-man or one-woman shows,” said Jessica Weinstock Paredes, a researcher at the National Registry of Exonerations.