Federal authorities are reportedly eyeing a second suspect in the murder of James “Whitey” Bulger.

Paul J. DeCologero, of the North Shore organized crime group, is believed to have taken part in the vicious Tuesday morning prison beating, according to the Boston Globe.

Law enforcement officials “with knowledge of the matter” told the newspaper that he and former Mafia hitman Fotios “Freddy” Geas set upon Bulger less than 12 hours after he arrived at Hazelton federal penitentiary in West Virginia.

The two men allegedly beat him to death inside his cell with a padlock stuffed inside a sock.

Geas confessed to killing the wheelchair-bound Bulger — Boston’s most famous crime boss — but said he did it alone.

Officials told the Globe that it was unclear how he and DeCologero found out about Bulger’s arrival at the prison, which has a reputation for being dangerous.

“It’s a very violent facility and it’s not a place that would be OK,” explained Richard Heldreth, president of Local 420 of the Federation of Government Employees, which represents correctional officers.

“Just knowing what everybody knows about him from media, movies and Wikipedia, it seemed very odd,” he said.

Heldreth told the Globe that despite some people’s suspicions, he was certain that officers had not been tipped off about Bulger’s transfer.

“They didn’t know until he came in,” he said. “I haven’t heard of anything being said like, ‘Watch him. Make sure he stays away from that guy.’”

DeCologero is serving a 25-year sentence on racketeering and witness tampering charges. Law enforcement officials are reportedly stumped about a possible motive for him in the Bulger killing but did note how DeCologero’s conviction was secured thanks to the testimony of several former partners — including his own father — who flipped and became government witnesses.

The mobster had also been busted for ordering the hit of 19-year-old Aislin Silva, who was killed and dismembered out of fear that she’d cooperate with police and testify, according to the Globe.

Police sources told the newspaper that DeCologero and Geas both know each other but never crossed paths until they got to prison.

“Paul J. was nothing more than a low-level drug dealer who was himself drug-addicted and who sometimes acted as a puppet for his dominant uncle,” defense attorney John Wall wrote in his sentencing memorandum.

“Paul J.’s involvement with his family’s life of crime and drug abuse was early and involuntary. Both of his parents were drug addicts and drug dealers,” Wall added. “He was physically abused by his father and others. He saw his father physically abuse his mother [and] never had a positive role model or a support system of any kind.”

DeCologero and Geas were both in general population when Bulger was placed there Tuesday, much to the surprise of prison staff.

“Why did he come here in the first place and why was he put in general population?” Heldreth asked. “That’s the most burning question of all.”