Though Bulger is known to have medical issues, it's not clear why he was on the move, the Boston Herald reported.
The 89-year-old, who was serving a life sentence for killing at least 11 people, had moved to the maximum security Hazelton Penitentiary in Bruceton Mills, federal officials told NBC News.
West Virginia News had confirmed through the president of Local 420 of the American Federation of Government Employees, Richard Heldreth, that a murder had taken place at the prison on the morning of October 30.
Mob boss James "Whitey" Bulger has been killed after being moved to a new prison, according to U.S. media.
Last week, he was transferred out of a federal prison in Florida to the one in Oklahoma City.
Bulger's attorney, Hank Brennan who tried to appeal his life sentence all the way to the U.S. Supreme Court, declined to comment to the Boston Herald pending notification of Bulger's death by the Bureau of Prisons. Weadick was convicted in June 2018 of the 1993 murder of Steven DiSarro, a South Boston business owner. The Hazelton prison where he died is "one of the federal system's roughest prisons", reports the West Virginia newspaper. She was captured with Bulger in Santa Monica in 2011.