David Ranta, who prosecutors said was the victim of a bungled investigation, had been convicted of killing Chaskel Werzberger, a Brooklyn rabbi, during a failed jewel robbery in 1990. He was exonerated and released Thursday.
His lawyer, Pierre Sussman, told ABC News Ranta suffered a massive heart attack Friday night and was being treated at a New York hospital.
Ranta, 58, had been with his family following his release in a New York courtroom Thursday. Sussman did not say where Ranta was being treated, ABC reported.
Charles J. Hynes, who had just become Brooklyn district attorney when Werzberger was killed, asked a court to release Ranta -- who was an unemployed printer with a drug problem when witnesses identified him to investigators as having participated in the murder. Witnesses subsequently said they had been coached by the lead detective on the case, Louis Scarcella, The New York Times reported.
Scarcella said Ranta confessed to the crime 26 hours after his arrest, a confession Ranta says he never made.
"I said from the beginning I had nothing to do with this case," Ranta said Thursday as he left the courthouse.
Prosecutors have said Werzberger's killer is likely a man who died two months after Werzberger was killed. They have not identified him.