FILE - This June 23, 2011, file booking photo provided by the U.S. Marshals Service shows James

BOSTON (AP) — A death certificate confirms that notorious Boston crime boss James "Whitey" Bulger died of blunt force injuries to the head in prison last year.

The document obtained by NBC Boston says the 89-year-old Bulger was "assaulted by other(s)" and was found in his cell at 8:21 a.m. Oct. 30.

Bulger was serving a life sentence for 11 murders and other crimes when he was beaten to death in his prison cell, hours after he was transferred to a West Virginia prison.

Bulger became one of the nation's most-wanted fugitives after fleeing Boston in late 1994. He was captured in 2011.

No charges have been filed in Bulger's death, but officials have said two Massachusetts mobsters are under suspicion in his killing.