Aaron Josefczyk / Reuters Ariel Castro (L), 53, enters the courtroom in Cleveland, Ohio in this July 26, 2013 file photo. Castro, the Cleveland man sentenced to life in prison for the abduction, rape and torture of three women, was found dead in his Ohio jail cell, according to a prison official on September 3, 2013. REUTERS/Aaron Josefczyk/Files (UNITED STATES - Tags: CRIME LAW OBITUARY)

Cleveland serial rapist Ariel Castro may have died by accident, not suicide, according to a new report that detailed the falsification of prison logs and suggested that the kidnapper may have been engaged in auto-erotic asphyxiation in his cell.

Castro was serving a life sentence plus 1,000 years after pleading guilty to the decade-long imprisonment of Gina DeJesus, Amanda Berry and Michelle Knight. The 53-year-old former bus driver was found hanging in his cell a month into his term.

He was found on Sept. 3 with his pants and underwear around his ankles at 9:18 p.m., hanged by his neck with a bed sheet from his cell window, according to the report released Thursday by the Ohio Department of Rehabilitation and Correction.

Castro left no suicide note, according to the report. He had pictures of his family out in his cell and a Bible open to the Gospel of John, chapters 2 and 3.

“These facts, however, were relayed to the Ohio State Patrol for consideration of the possibility of auto-erotic asphyxiation,” the report states. “No other immediate observations about the scene led to conclusions about the motivation for the self-inflicted death.”

Investigators also reviewed “incoming letters to Castro that were found in his property … and found no additional information that would lead to conclusions about the motivation for the self-inflicted death.”

David Maxwell / EPA A view of the demolition of the house of convicted kidnapper and rapist Ariel Castro, on Seymour Avenue in Cleveland, Ohio.

Castro had been reviewed by a mental health professional in early August, completed a mental health evaluation, and completed a suicide questionnaire, according to the report. “He indicated no current suicidal thoughts or past attempts to hurt himself,” the report said. Family members visited on Aug. 12 and Aug. 26.

“There seems to be no known, substantiated motivation for the self-inflicted death,” the report concludes.

The report also found that 30-minute rounds were not properly completed on Castro’s cell at eight points during the afternoon and evening leading up to his death, with records for five of those rounds falsified in prison logs.

The two officers who appear to have falsified log records have been put on administrative leave, according to the report.

However, rounds were conducted at 8:45 p.m. and then again at 9:15 p.m., at which point Castro was found.

After Castro was found, prison staff cut him down and administered CPR until medical responders arrived, the report said. He was transported by ambulance to Ohio State University Medical Center, where he was pronounced dead at 10:52 p.m.

Castro left documents titled “Informal Complaints” in his prison cell, in which he wrote that he suffered “verbal harassment” from prison staff and inmates, and expressed fears that someone was meddling with his food. The documents show that “Castro’s paranoia about his food led him not to eat some of his meals.”

The complaints about his food “appear to be unjustified,” the report says.

In September, family members reacted with surprise to Castro’s death so soon after he was sentenced.

“My anger with him kept me from visiting him in prison, even when he was moved to a facility just 20 minutes away from my doorstep,” the kidnapper’s son Ariel Anthony Castro wrote in the Cleveland Plain Dealer on Sept. 21. “Coping would have to come before any possibility of a change of heart. But after mere weeks, that window slammed shut.”

NBC News’ Mark Stevenson and Hasani Gittens contributed to this report.

Related: