According to a report from the Ohio Department of Rehabilitation and Correction, the 53-year-old Castro was found with his pants and underwear pulled down to his ankles.
"Castro left no suicide note and had previously shown no suicidal ideations in multiple levels of assessment," the report stated.
The state forwarded those facts to police to consider the possibility of auto-erotic asphyxiation, whereby individuals achieve sexual satisfaction by briefly choking themselves into unconsciousness.
It was also revealed in the report that prison guards failed to check on Castro in the hours before he killed himself on Sept. 3 and falsified observation logs.
Castro was only a few weeks into a life sentence after pleading guilty in August to kidnapping three women from the streets of Cleveland, then imprisoning them in his home for a decade. He repeatedly raped and beat them, limiting their access to food and toilet facilities and chaining them at times to a pole in the basement. Rescued with the three women in May was a 6-year-old girl Castro fathered with one of the victims.
The Associated Press contributed to this report.