Cuyahoga County Sheriff's Office Ariel Castro on May 7, 2013, one day after his arrest

A new investigation into kidnapper Ariel Castro’s death suggests prison guards may have falsified information regarding his supervision before his death, and that the actual cause may have been something known as auto-erotic asphyxiation, not suicide.

The investigation arose from allegations of prison guard misconduct surrounding the death of Castro, who pleaded guilty to keeping three women hostage in his Cleveland home for years, the Columbus Dispatch reports. Prison guards allegedly didn’t complete their supervision rounds and faked logs and records surrounding the infamous kidnapper’s death.

Investigators from the Ohio Department of Rehabilitation and Correction noted that Castro was found hanging from prison a window hinge with his pants and underwear at his ankles on Sept. 3. They are now considering the possibility that Castro died from auto-erotic asphyxiation, a masturbation technique involving self-strangulation. Commonly known as AEA, the practice involves cutting off oxygen to the brain in order to intensify orgasms during masturbation or sex.

AEA deaths are often confused with suicide, and initial reports suggested that Castro’s death was also a suicide. But officials noted that Castro displayed no suicidal tendencies and did not write a suicide note.

Castro pleaded guilty to nearly 1,000 counts of kidnapping, rape, aggravated murder (forcing his victims to miscarry) and other crimes. He was sentenced to life without parole, plus 1,000 years, but had only served four weeks of his sentence at the time of his death.

[Columbus Dispatch]