The parole board made its decision after a key witness to the playground shooting recanted. The witness, Sharron Ivory, told Ms. Busby, and then investigators from the district attorney’s office, that detectives had coached him on which person to pick out. Mr. Ivory was also able to demonstrate that in the months before the trial, he had amended his account of the killing to coincide with details that the police provided, such as the kind of gun an assailant had used.

“I sent in a notarized affidavit with an apology to this man for lying on him and for helping a dirty cop taking this man’s life from him,” Mr. Ivory, who is in prison in connection with an unrelated homicide, wrote to the parole board. His recantation was especially valuable because the victim was his cousin.

Ms. Busby also sent the board an affidavit declaring Mr. Moses’ innocence that was signed by one of the men who had participated in the crime but had been acquitted. Because of the acquittal, that defendant cannot be retried.

Lawyers say preparing a parole application based on a claim of innocence is risky, because parole boards want to see inmates say they are sorry. A defendant who lacks remorse is considered more likely to commit other crimes. Indeed, a guilty person who pretends to be remorseful is more likely to be released than a person who says he did not do it, said Daniel S. Medwed, a Northeastern University professor who has studied the issue.

“It is grounded in the 19th-century quasi-religious belief that you have to come to Jesus and admit your sins to be saved,” Professor Medwed said. “Therefore, a prisoner who claims innocence has no real reason for doing it. It’s going to hurt you more than help you.”

The parole board has, in isolated instances, granted parole to inmates who claimed innocence, suggesting a growing acknowledgment of the possibility of wrongful convictions, Professor Medwed said.