BOSTON • James "Whitey" Bulger, who lived a double life as one of Boston's most notorious mobsters and as a secret FBI informant before going on the run for 16 years, was killed at a federal prison in West Virginia, sources say.
The Federal Bureau of Investigation (FBI) was looking into Bulger's death and a prison employee briefed on the matter said on Tuesday it was being investigated as a homicide.
A Bureau of Prisons statement had earlier confirmed that Bulger - portrayed by Johnny Depp in the 2015 film Black Mass - had died and said the FBI was investigating.
Bulger, who was 89, had been transferred a day earlier to the high-security prison in a wheelchair, the prison employee said.
Two men were seen on surveillance footage entering his cell, the prison employee said.
Bulger's body was discovered wrapped in a sheet, the prison employee said, and the notorious gangster had been beaten so badly blood had come out of his ears.
Federal officials did not give a cause of death, but the Bureau of Prisons said no other inmates or staff were injured.
The prisons bureau had said in its statement that Bulger's body was found on Tuesday. The prison employee said it was discovered when Bulger did not appear for breakfast, indicating that he was killed early morning or overnight.
Mr Henry Brennan, a defence lawyer for Bulger, said in an e-mail he could not confirm or deny the reports.
James Bulger's body was discovered wrapped in a sheet, the prison employee said, and the notorious gangster had been beaten so badly blood had come out of his ears.
Bulger was convicted in August 2013 of 11 murders, among other charges, and sentenced to two consecutive life terms plus five years.
Prison had been something Bulger had gone to great lengths to avoid - killing potential witnesses, cultivating corrupt lawmen and living as a fugitive for 16 years.
It all ended when a tip from a former Icelandic beauty queen led to his capture in June 2011 in Santa Monica, California, where he was living with a long-time girlfriend.
Bulger and his Winter Hill gang had operated for more than two decades in the insular Irish-dominated South Boston neighbourhood, engaging in loan sharking, gambling, extortion, drug dealing and murder.
They did so with the tacit approval of an FBI agent who looked the other way when it came to Bulger's crimes so that he would supply information on other gangsters.
Bulger was feared for his short temper and brutality. Prosecutors said he strangled two women with his hands and tortured a man for hours before shooting him in the head with a machine gun.
The US Justice Department paid more than US$20 million (S$27.7 million) in damages to families of victims killed by Bulger on the grounds that he was operating under government supervision while killing people.
While Bulger was robbing banks and killing people, his younger brother Billy was acquiring political notoriety and power.
His brother served in the Massachusetts legislature for 35 years, after which he was president of the University of Massachusetts.
He was forced to resign the latter job in 2003 after it was learnt that eight years earlier he had spoken by telephone with his brother, who at the time was a federal fugitive, and did not report it to the authorities.