New details are emerging about the death of notorious mob boss Whitey Bulger on Tuesday after he was transferred to the general population of U.S. Penitentiary Hazelton, one of the most dangerous prisons in America.

Bulger ― who ruled Boston’s criminal underground for more than 20 years and stayed on the run for another 16 before his capture ― was reportedly beaten to death within hours of his transfer from a Florida prison to the high-security penitentiary in West Virginia on Tuesday.

Federal Bureau of Prisons officials say one of the weapons used to murder him was a lock in a sock. Bulger was in a wheelchair when “several potential suspects” beat him to death, officials told NBC. The lock in a sock is a particularly grisly method, which involves a lock placed in a sock and swung like a mace.

So far, federal officials have been dodging questions about who transferred Bulger and why. But reports by HuffPost and The Boston Globe suggest that whoever did so was throwing him into the lion’s den. There were plenty of inmates at Hazelton who hated him.

One of the suspects in Bulger’s murder was Fotios “Freddy” Geas, who had a longtime beef with Bulger and believed the gangster had helped frame one of his friends for murder, according to a harrowing report by the Globe.

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As the newspaper reports, the Bureau of Prisons might have known that throwing Bulger into the general population at Hazelton would immediately pit the 89-year-old against some of his enemies:

Because Bureau of Prisons officials have refused to answer questions about Bulger’s murder, it remains unclear why the presence in Hazelton’s general population of Geas and at least one other Massachusetts organized crime figure, Paul Weadick, didn’t set off alarm bells that this was not a safe place for the elderly hood.

Other prison officials told HuffPost’s Lauren Weber on Wednesday that whoever transferred Bulger in the first place “screwed up.”

“I don’t know who picked Hazelton ― it’s one of our most violent institutions,” said Joe Rojas, union president for correctional staff at Coleman penitentiary in Florida. Bulger had been incarcerated at Coleman for four years.

“Sending him there is like a death sentence. It’s like going on death row,” he added.

Bulger, the leader of Boston’s Winter Hill Gang, killed or arranged to kill nearly 20 people between 1973 and 1985, HuffPost’s David Lohr reports. He evaded capture for 16 years after he was added to the FBI’s Ten Most Wanted list, hiding in plain sight with longtime companion Catherine Greig, along with $800,000 in cash and a stash of weapons. He was captured in 2011.