Prison officials today confirmed that the 53-year-old died late last night (Tuesday).
A spokeswoman for the Ohio Department of Rehabilitation and Correction said:
‘He was housed in protective custody which means he was in a cell by himself and rounds are required every 30 minutes at staggered intervals.
‘Upon finding inmate Castro, prison medical staff began performing life saving measures. Shortly after he was transported to [the prison medical facility] where he was pronounced dead at 10:52 pm.
‘A thorough review of this incident is under way.’
Castro was charged with aggravated murder, multiple counts of kidnapping and the rape of three women held for a decade, and sentenced to life imprisonment without parole plus 1000 years on the 1 August.
The divorced father abducted Michelle Knight, now 32, Amanda Berry, now 27, and Gina DeJesus, now 23, from the Cleveland streets between 2002-04.
Castro then spent 11 years raping and torturing the three women, who he kept locked up in his basement, even fathering a child with Berry.
At his sentencing, Castro told the court that he had been "driven by sex", adding:
‘I'm not a violent predator… I'm not a monster, I'm a normal person.
‘I'm just sick. I have an addiction, just like an alcoholic has an addiction.’
However Knight hit back at his plea, revealing how the former bus driver went to church every Sunday, before coming home to ‘torture’ his victims.
‘I spent 11 years in hell. Now your hell is just beginning. You will face hell for eternity.
‘From this moment on, I will not let you define me, or affect who I am. I will live on, you will die a little every day.’