(CNN) Union leaders and a former federal corrections official are questioning the timing of James "Whitey" Bulger's transfer last month from a Florida prison to the US Penitentiary Hazelton, where he was returned to the general inmate population.

Bulger was brutally beaten to death in the West Virginia prison, according to a federal law enforcement official with knowledge of the investigation. Investigators believe Bulger was attacked by more than one person. At least one inmate involved in the beating has ties to organized crime in Massachusetts, the official said.

Joe Rojas, president of American Federation of Government Employees (AFGE) Local 506 at the Federal Correctional Complex in Coleman, Florida -- where Bulger was previously housed -- said prison officials "dropped the ball" by transferring him to the notoriously violent Hazelton facility and mixing him with the general population.

"It's like sending somebody to death row," Rojas, who was not involved in the decision to transfer Bulger, told CNN.

At the end of his violent life, feared former mob boss Bulger was an 89-year-old lifer confined to a wheelchair and suffering from a heart condition and other ailments, according to US Bureau of Prisons records and interviews with union officials.

Records indicate adjustment in care requirements before transfer

BOP records obtained by CNN state that Bulger suffered from high blood pressure, aortic stenosis and prostate and bladder problems.

A previous request made by officials at Coleman to transfer Bulger was denied in April. Records show the request was coded to indicate Bulger required a higher level of medical care, or Care Level 4 , for inmates who are severely impaired and may require daily nursing care.

It's not clear why the April transfer request was denied. In October, however, a transfer request was approved and coded to indicate he no longer needed to be in a medical facility.

The records show Bulger's "medical/physical treatment" was completed and that he was to be transferred to the general population at Hazelton under Care Level 2 , a lower medical classification for inmates who are stable outpatients that require at least quarterly clinician evaluation.

Rojas said if Bulger was dropped to Care Level 2, that would be strange.

"I don't care who you are, you can't justify dropping him ... to a 2. ... He's always going to be (at least) a Care Level 3 because of his age and he's in a wheelchair" with heart problems, Rojas said.

"The only way you drop him to a Care Level 2 is to get rid of him," Rojas said. "Their intent was to get rid of him, probably because he was a crusty old man and a pain in the ass."

Rojas said he does not believe it was anyone's intent at BOP to get Bulger killed, but the transfer had the effect of "sending him to die at Hazelton."

"There's no conspiracy to try to get him killed," Rojas said. "Nobody wants to get another inmate killed."

Rojas said Coleman had appeared to be a good fit for Bulger in two ways: First, Coleman is well prepared to care for inmates with medical needs. Second, the Coleman facility is what's known as a "closed yard," considered a safer type of prison, and houses higher-profile prisoners such as Bulger, informants and former gang members.

Apart from its reputation for violence, he said, Hazelton houses current gang members and mafia figures.

"We all know that you can't put somebody like (Bulger) -- high profile -- there," Rojas said. "It's like throwing meat to a bunch of sharks."

Former warden also questions move

Cameron Lindsay, a former warden at five Bureau of Prisons facilities who said he had no direct knowledge of the case, also questioned the timing of Bulger's transfer.

"The BOP intentionally designated and transferred Bulger with the belief in mind that he could walk the line at Hazelton, meaning he could be placed in the general population there," he told CNN.

"This is astounding given the fact that Bulger is a super high publicity case, as he's one of America's most infamous criminals."

The Federal Bureau of Prisons said it doesn't disclose the reasons for specific inmate transfers.

"Per BOP policy, the designation process includes a review (that includes) whether there exists any known safety threat from other inmates," the prisons bureau statement said.

"There were no known threats to Mr. Bulger from other inmates upon designation to the Hazelton facility."

The bureau website lists factors considered when designating inmates to correctional institutions, including security, population, and medical needs.

"It was really odd that he was general population (at Hazelton) given his notoriety and who he was. I was pretty surprised," said Richard Heldreth, President of the American Federation of Government Employees Local 420, which represents staff at Hazelton.

Lindsay said, "I don't think that any nefarious plot was afoot. That would be terribly inconsistent with what I know about the Bureau of Prisons. I think it's more -- I'm going to guess it's an issue of complacency. Somebody was asleep at the switch."

Two other prisoners were stabbed to death in fights with fellow inmates this year at US Penitentiary Hazelton -- one in April, and one on September 17, according to a letter sent by members of Congress to then-Attorney General Jeff Sessions.

With Bulger's death, three Hazelton inmates have now been killed there in seven months. Few details have been released and prison officials have not disclosed whether they believe factors such as increased staffing would have made a difference.

Records show Bulger got in trouble at Coleman this year

The Bureau of Prisons records obtained by CNN show the former South Boston mobster was less than a stellar prisoner.

In March -- one month before the first attempted transfer -- Bulger was found guilty of "conduct which disrupts -- most like threatening staff," according to the records.

Rojas said Bulger was sentenced to 30 days in a special housing unit in March after threatening a nurse in February with the warning, "Your day of reckoning is coming."

Bulger also had been found guilty in 2015 of masturbating in front of male staff, the records show.

Bulger was housed at Coleman since 2014 and accumulated just the two infractions, Rojas said.

At Coleman, Bulger had "butlers," or younger prisoners who would bring him lunch and do other tasks for him, according to Rojas. Bulger would compensate these men by giving them commissary stamps, and by other means.

The ex-mobster was generally "harmless at Coleman," Rojas said.

Rojas said transfers to tougher prisons generally follow repeated infractions for offenses such as stabbings or fighting.

Bulger laid to rest on Thursday

A private funeral Mass was held for Bulger on Thursday at St. Monica-St. Augustine Church in South Boston, according to a statement from the Catholic archdiocese. His burial was also private.

"Out of respect for the family and those who were hurt, it was a private service just for the immediate family," Father James A. Flavin, the pastor, said in the statement.

"The Church is a spiritual home for any person or family seeking God's Wisdom and peace in a time of crisis and grief. The Church is certainly aware of the deep pain that innocent victims of crime and violence live with every day."

Flavin, in his homily, said: "We pray that everyone is able to feel the peaceful presence of God and His son Jesus in the midst of chaos and pain."

Bulger, who eluded federal authorities for more than 16 years before his arrest in June 2011, was serving the rest of his life in prison for a litany of crimes that included his role in 11 murders.

He was sentenced in November 2013 to two life terms plus five years as architect of a criminal enterprise that, in the words of a federal judge, committed "unfathomable" acts that terrorized a city.

The US Penitentiary Hazelton is a high-security facility housing 1,270 male offenders at Federal Correctional Complex Hazelton.

One of the two suspects in the brutal beating was identified as Fotios "Freddy" Geas, a Mafia hit man from Massachusetts, The New York Times has reported, citing unnamed sources. It said Geas was moved to solitary confinement after the killing.

Geas, 51, is serving a life sentence at the same prison for the 2003 murder of a crime boss and another man he believed was an FBI informant.