COLUMBUS, Ohio (AP) -- Cleveland kidnapper Ariel Castro may have died from auto-erotic asphyxiation, not suicide, and two prison guards falsified logs documenting their observation of him in the hours before he died, the state said Thursday. Castro's pants and underwear were pulled down to his ankles when he was found, leading the state to forward those facts to the state highway patrol to consider the possibility of auto-erotic asphyxiation, according to the report from the Ohio Department of Rehabilitation and Correction. The report suggests -- but does not conclude -- that Castro may have died as the result of auto-erotic asphyxiation, whereby individuals achieve sexual satisfaction by briefly choking themselves into unconsciousness. Castro did not leave a suicide note and "multiple levels of assessment" did not find tendency toward suicide, the report said. A comprehensive mental health evaluation found "no evidence of serious mental illness or indications for suicide precautions were present," according to the report. Surveillance video indicates guards did not do at least eight required checks on Castro the afternoon and evening before he died. Two checks were done properly just before Castro hanged himself on Sept. 3 at a prison reception center south of Columbus. The report also said an ambulance contracted to provide medical assistance at the prison was significantly late in arriving, but the delay likely didn't affect the outcome. The report also said staff failed to make sure Castro watched a suicide prevention video when he first arrived in August. Castro, 53, was 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 during which time he repeatedly raped and beat them. He was accused of 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.