The Boston Globe reported Sunday Ellen Zucker, attorney for Calvin Carnes, asked the state's Supreme Judicial Court for a new trial Friday after receiving the documents last week.
Carnes is serving life in prison for killing four young men in a basement in Boston's Dorchester neighborhood in 2005.
"We have to do better than to let a DA [district attorney] sit for months and months and not inform the defendant that there is strong exculpatory evidence that could suggest he was wrongly convicted,'' Zucker said.
An unnamed prisoner said in a sworn document given the district attorney's office in February 2009 that Robert Turner, who was sentenced to 13 years in prison after confessing to being an accessory to the killings, had bragged in prison that he set up Carnes.
"He ... stated that he lied to the police to receive leniency and blamed the actual shootings on his co-defendant,'' the prisoner said. "Turner told me that he solely planned and executed four of his friends in a dispute over an AK assault rifle.''
Turner's lawyer, Michael Bourbeau, said the prisoner who made the allegation against Turner is a "jailhouse snitch'' trying to improve his own situation. The inmate is serving life in prison for murder.
"The story isn't about any allegations that Mr. Turner confessed, because there is no truth to that at all," Bourbeau said.
Suffolk District Attorney Daniel F. Conley said his office investigated the new information, determined it was not credible and then turned it over.