(Hazelton, WV) -- Former Boston mob boss James "Whitey" Bulger's death is officially being investigated as a homicide. The U.S. Attorney's Office and the FBI are looking into the matter, according to a statement from federal prosecutors in West Virginia on Wednesday. Bulger was found unresponsive in a federal prison in that state on Tuesday morning, just hours after he had transferred. The Boston Globe reports western Massachusetts mob figure Fotios "Freddy" Geas is the prime suspect in the murder.