Castro's Sept. 3 death was likely not the result of autoerotic asphyxiation, in which individuals choke themselves into unconsciousness to achieve sexual satisfaction, according to the consultants' report. An earlier review by the state prisons agency suggested that possibility.
The new report said all available evidence pointed to suicide, including a shrine-like arrangement of family pictures and a Bible in Castro's cell, an increasing tone of frustration in his prison journal and the reality of spending the rest of his life in prison while subject to constant harassment.
Subsequent reviews by the Ohio State Highway Patrol and the Franklin County coroner reached the same conclusion, the report said.
"Based upon the fact that this inmate was going to remain in prison for the rest of his natural life under the probability of continued perceived harassment and threats to his safety, his death was not predictable on September 3, 2013, but his suicide was not surprising and perhaps inevitable," the report said.
The consultants said it was likely Castro was harassed by guards, based on interviews with inmates who said they had heard it.
"I don't know if I can take this neglect anymore, and the way I'm being treated," Castro wrote in a journal on Aug. 22, according to the report.
"I will not take this kind of treatment much longer if this place treats me this way," Castro wrote on Aug. 31. "I can only imagine what things would be like at my parent institution. ... I feel as though I'm being pushed over the edge, one day at a time."
Castro was housed at the state's Correctional Reception Center south of Columbus before being sent to a permanent prison. None of the multiple health assessments he received indicated anything that would have required suicide-prevention measures, the consultants said.
Messages left Tuesday with Castro's attorneys seeking comment about the report weren't immediately returned.
The Ohio Department of Rehabilitation and Correction is committed to following recommendations in the report, spokeswoman JoEllen Smith said in a statement.
They include beefing up staff training on suicide prevention and ending the use of online training.
Ohio prison inmate suicides were below the national rate over the past five years but above the national rate this year alone, the study found.
"We take life very seriously," said Stuart Hudson, the prison system's managing director of health care and fiscal operations. "We don't want to see a single suicide out of our population of more than 50,000 inmates."
Castro, 53, was found kneeling in his cell with his pants down and hanging from a sheet attached to a window hinge, according to an earlier prisons report. He had just begun serving a sentence of life plus 1,000 years. He pleaded guilty in August to imprisoning three women in his Cleveland home for a decade while repeatedly raping and assaulting them. He fathered a girl with one of the victims.
Some inmates - who had not seen Castro - suggested his pants slipped because of his 10-pound weight loss since entering prison, the report said. But one nurse interviewed by the consultants said Castro was completely naked, while a supervisor said it was not uncommon for Castro to be nude in his cell, according to the report.
Castro was also naked on occasion in Cuyahoga County Jail, where he was housed before pleading guilty and being sentenced, according to jail logs.
Two prison guards were placed on paid administrative leave during the state's investigation into Castro's death. The corrections department alleged they falsified logs documenting the number of times guards checked on Castro before he died.
Those two guards and an additional one received formal warnings Monday that any future violations would result in immediate firings that can't be challenged.
The consultants' report criticized the falsification but said it didn't contribute to Castro's death since he was seen alive minutes before he hanged himself in a check that met prison standards.
The union representing prison guards says the state is scapegoating front-line employees for supervisory failures.
Castro abducted the women from the streets of Cleveland from 2002 to 2004 when they were 14, 16 and 20. He periodically kept them chained in rooms, sometimes in the basement, and restricted access to food and toilets.
The women were rescued May 6 when one of them broke out part of a door and called for help.
Castro told a judge at sentencing that he suffered from addictions to sex and pornography. "I'm not a monster. I'm sick," he said.