James "Whitey" Bulger, shown in this June 2011 booking photo, was killed just hours after being transferred to the US Penitentiary Hazelton in West Virginia in 2018.
CNN  — 

Three inmates charged in the violent killing of notorious Boston mob boss James “Whitey” Bulger while imprisoned with him in West Virginia have accepted plea agreements, court filings show.

Fotios Geas and Paul J. DeCologero are accused by prosecutors of bludgeoning Bulger to death as fellow defendant Sean McKinnon acted as a lookout in October 2018, just hours after the gangster was transferred to the US Penitentiary Hazelton in Bruceton Mills.

The three men have agreed to plead guilty, according to motions filed by prosecutors Monday. The filings do not indicate to which counts they are pleading but say the defendants “agree to cooperate with the United States Probation Office.”

Each of the men had been charged with conspiracy to commit first-degree murder. Geas and DeCologero also face first-degree murder and assault charges, according to the filings. McKinnon was charged with making false statements to a federal agent regarding what he knew about Bulger’s murder.

A federal judge must approve the plea agreements. Prosecutors are asking for the court to schedule a change of plea hearing, combined with a sentencing hearing.

Bulger ruled over Boston’s infamous Winter Hill gang during the 1970s and ’80s, committing what a judge would later describe as “unfathomable” acts that terrorized the city.

He became one of the most wanted men in America as he evaded arrest for 16 years on racketeering and murder charges, gaining him a spot on the FBI’s most-wanted list. Bulger was finally arrested in 2011 and sentenced to life in prison in 2013 after a jury concluded he was responsible for 11 killings, among other crimes.

His criminal reign inspired Jack Nicholson’s character in Martin Scorsese’s 2006 film, “The Departed.”

“He lived violently and he apparently died violently,” said Dick Lehr, author of “Whitey: The Life of America’s Most Notorious Mob Boss” when Bulger was killed at age 89. “It marks the full circle of a terrible life.”

Bulger’s family sued prison employees after his death, alleging prison wardens and other correctional officers were “intentional or deliberately indifferent” to the danger Bulger faced in prison, and it appeared Bulger was “deliberately sent to his death.” A judge dismissed the lawsuit in January 2022.

However, a December 2022 report by the Justice Department’s Office of the Inspector General detailed a series of missteps by prison officials that may have put Bulger at risk when he was transferred to the West Virginia facility.

Among the mistakes outlined was the decision to place Bulger – one of the most well-known organized figures at the time – into the general population after prison guards spoke of his impending arrival in the presence of inmates.

Inmates’ prior knowledge of his arrival, the report says, dramatically increased the likelihood Bulger faced imminent harm at Hazelton. Recorded phone calls and emails at the time included in the report show how inmates were prepared for what might happen when Bulger arrived.

In the report, one inmate interviewed said because other inmates had a “beef” with Bulger and because he was viewed as a “rat” for working with the FBI, “both the inmates and the staff were speculating about – and inmates were betting money on – how long Bulger would stay alive at Hazelton.”

CNN’s Hannah Rabinowitz, Ray Sanchez and Kristina Sgueglia contributed to this report.