Prison spokeswoman JoEllen Smith is cited as saying that Ariel Castro was found hanging in his cell at 9:30pm (2:30am UK time) last night.
Prison medical staff performed CPR before he was transported to a hospital, where he was pronounced dead, she said.
Castro was sentenced to life in prison plus 1,000 years after pleading guilty to 937 counts including kidnapping and rape.
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The banking group has also allocated £283m towards tackling its mistreatment of people in mortgage arrears.
Thursday will be a breezy day with sunshine and blustery showers developing for most of us.
She had been with friends at the station at 11pm the previous evening. Officers are now working to find out how she ended up on the tracks.