“It’s really just about basic fairness,” said Scott Levy, the special counsel to the Bronx Defenders’ criminal defense practice.

Defense lawyers said the old system too often ensnared people like Terrell Gills, who spent 18 months in jail accused of robbing a Dunkin’ Donuts in Queens before prosecutors revealed that another man had confessed to robbing two nearby locations the same day, evidence that led to his swift acquittal.

In another Queens case, Romeo Martinez, an undocumented immigrant, spent two years in Rikers awaiting trial on robbery charges before the district attorney turned over the name and telephone number of a city firefighter who had seen what happened and had called the police.

At trial, the firefighter gave testimony that contradicted the accounts of two men who claimed Mr. Martinez had tried to take their wallets and had slashed one of them with a knife. The two men had attacked Mr. Martinez, not the other way around, the firefighter said. A jury acquitted him in just a few hours.

Another trial that might have had a different outcome under the new rules was that of Donnell Genyard, who is serving a 19-year sentence for manslaughter, his lawyers said.

The Queens district attorney’s office waited until just before trial to hand over the names and addresses of two witnesses whose accounts raised doubts about Mr. Genyard’s guilt, his lawyers said.

The witnesses told the police they had seen the victim, Eartha Wilson, at least an hour after prosecutors said she was killed in a stairwell outside a party in Brooklyn in 2003. The jury never heard their testimony, and Mr. Genyard was found guilty of first-degree manslaughter in 2007.

“This trial could have looked very different,” Richard Joselson, of the Legal Aid Society, said.