OCALA, Fla. (AP) — A man charged in the prison killing of notorious Boston gangster James “Whitey” Bulger will remain behind bars while he awaits trial, a federal judge ruled Monday.

Sean McKinnon, 36, was on federal supervised release when he was arrested Thursday in Florida on charges including conspiracy to commit first degree murder.

Two other men charged in Bulger’s killing — Fotios “Freddy” Geas, 55, and Paul J. DeCologero, 48 — were already locked up.

The men are accused of conspiring to kill Bulger hours after he was transferred to USP Hazelton in West Virginia from a prison in Florida in 2018. Bulger, who served as an FBI informant and later became one of the nation’s most-wanted fugitives, had been serving a life sentence for 11 murders and other crimes.

Authorities say Geas and DeCologero struck Bulger in the head multiple times while McKinnon acted as a lookout. McKinnon is charged separately with making false statements to a federal agent. Prosecutors say he told federal agents he wasn’t aware of what happened to Bulger.

U.S. Magistrate Judge Philip Lammens in Florida granted prosecutors’ request to keep McKinnon detained until trial, calling him both a flight risk and a danger to the community.

Authorities have not revealed a possible motive for Bulger’s killing, which has raised questions about why the 89-year-old was moved to the prison nicknamed “Misery Mountain” and placed in its general population instead of more protective housing.

McKinnon, who was Geas’ cellmate at Hazelton, pleaded guilty in 2015 to stealing a dozen handguns from a Vermont firearms dealer. He was moved to a halfway house in February before being released from there in July.

An email seeking comment was sent to an attorney who represented McKinnon at his detention hearing on Monday.

DeCologero, who was in an organized crime gang led by his uncle in Massachusetts, was convicted of buying heroin that was used to try to kill a teenage girl his uncle wanted dead because he feared she would betray the crew to police. The heroin didn’t kill her, so another man broke her neck, dismembered her and buried her remains in the woods, court records say.

Geas, a Mafia hitman, and his brother were sentenced to life in prison in 2011 for their roles in several violent crimes, including the 2003 killing of Adolfo “Big Al” Bruno, a Genovese crime family boss in Springfield, Massachusetts.