FILE PHOTO: Former mob boss and fugitive James "Whitey" Bulger is seen in a combination of booking mug photos released to Reuters on August 1, 2011. REUTERS/U.S. Marshals Service/U.S. Department of Justice/Handout/File Photo ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY.

(Reuters) - U.S. prosecutors are investigating Boston gangster James “Whitey” Bulger’s death as a homicide, officials said on Wednesday, a day after his bloodied body was discovered at a West Virginia federal prison.

“The United States Attorney’s Office and the FBI are investigating the death of James Bulger as a homicide,” the U.S. Attorney’s Office for the Northern District of West Virginia said in a statement. The office declined to provide further details.

Bulger, 89, had lived a double life as one of Boston’s most notorious mobsters and as a secret Federal Bureau of Investigation informant before going on the run for 16 years. He was convicted in August 2013 of 11 murders, among other charges, and sentenced to two consecutive life terms plus five years.

A U.S. Bureau of Prisons statement said on Tuesday the FBI was looking into the death.

Bulger, whose life was depicted in the 2015 film “Black Mass” starring Johnny Depp, had been transferred a day earlier in a wheelchair to the high-security Hazelton penitentiary in West Virginia, a prison employee briefed on the matter said on Tuesday.

Two men were seen on surveillance footage entering Bulger’s cell, the prison employee said. Bulger’s body was later discovered wrapped in a sheet, the employee said, and had been beaten so badly that blood had come out of his ears.

He had been captured in June 2011, after a former Icelandic beauty queen tipped off authorities that he was living in Santa Monica, California.

The U.S. Justice Department paid more than $20 million in damages to families of people killed by Bulger on the grounds that he was operating under government supervision while killing.