Three men have been charged over the prison killing of infamous Boston gangster James “Whitey” Bulger.

The 89-year-old Bulger was discovered unresponsive in October 2018 at a maximum-security facility in West Virginia.

Fotios Geas, 55, Paul J DeCologero, 48 and Sean McKinnon, 36, were all charged with conspiracy to commit first-degree murder, the Justice Department said.

Bulger was captured in California in 2011 after a 16-year manhunt.

He was serving two life sentences for 11 murders when he was beaten to death, on the same day that he was transferred to the Hazelton penitentiary in West Virginia, which houses 1,385 inmates.

The US justice department announced the charges against the three men on Thursday.

Federal prosecutors accuse Geas and DeCologero of striking Bulger in the head multiple times, causing his death.