The sordid tale of Cleveland kidnapper and rapist Ariel Castro has taken another lurid turn, with officials saying dis death may have been caused by auto-erotic asphyxiation and a coroner insisting it was suicide.

The coroner was the same one who did the autopsy on Castro, who died in September at age 53 -- a month after he was sentenced to life in prison plus 1,000 years for holding three women captive and treating them like sex slaves for a decade.

It was an abrupt ending to a sordid case that shocked the United States and the world with revelations of depravity and brutality carried out in an ordinary Cleveland home.

Details of his death, previously thought to be suicide, were released in a report with the results of an Ohio state prison internal investigation.

Castro was found hanging from a hinge in the window of his cell by a sheet wrapped around his neck with his pants and underwear pulled down to his ankles.

"The relevance of this finding is unclear," the report concluded, adding that the details were "relayed to the Ohio State Highway Patrol for consideration of the possibility of auto-erotic asphyxiation."

But late Thursday, Franklin County coroner Paula Gorniak said in a statement there was no sign that Castro had been sexually stimulated, CNN and other news outlets reported.

"I did the autopsy myself. I saw the ligature. I saw the pictures of the cell. It was a suicide," CNN quoted the coroner as saying.

She said the fact that Castro's pants and underwear were at his ankles is not enough to back up the idea of auto-erotic asphyxiation.

The garments may have simply fallen down while he was hanging, she wrote.

Gorniak said no one involved in the Ohio corrections report consulted her on its report on the possible cause of death and she was not pleased with this.

Castro had left no note and given no indication of suicidal tendencies, the corrections report noted, adding that "no other immediate observations about the scene led to conclusions about the motivation for the self-inflicted death."

The investigation also found that prison guards failed to check on Castro every 30 minutes as required and then falsified their logs.

However, video surveillance cameras showed that guards performed the required check at 8:45 pm and again at 9:15 pm when he was found hanged in his cell.

Castro's crimes -- committed when he imprisoned the women in a so-called 'house of horrors' -- led to an outpouring of national pity for the three victims, Amanda Berry, now 27; Gina DeJesus, 23; and Michelle Knight, 32.

They were abducted separately between 2002 and 2004 at the ages of 14, 16, and 20 and held captive in a working class neighborhood of Cleveland.

His three victims escaped on May 6 when Berry managed to break open part of the front door and call out to a neighbor for help. She emerged from the dilapidated house with a young daughter who was fathered by Castro during her captivity.

More than 92 pounds (42 kilos) of chains were found in the filthy, darkened home where the women were kept in locked rooms with boarded-up windows.

The house was demolished a few days after Castro was sentenced.

Castro pleaded guilty on August 1 after prosecutors agreed not to seek the death penalty.

A tearful Michelle Knight said in emotional testimony before the court that death would have been "so much easier" for her tormenter.

"I spent 11 years in hell, and now your hell is just beginning," Knight told Castro.

In a rambling quasi-apology to his victims -- only Knight was present in the courtroom -- Castro claimed he had acted on impulse as a result of sexual addiction.

"I'm not a monster. I'm sick," he said then, clad in an orange prison jumpsuit.

Despite having pleaded guilty to 977 charges related to his victims' brutal ordeal -- including terminating Knight's pregnancies by starving and beating her -- Castro insisted he was not a violent man and that "there was harmony in that home."