Ariel Castro, sentenced to life in prison for holding three women captive and raping them for a decade, has been found dead in his prison cell, news reports say.

The former school bus driver, who was sentenced to life in prison last month, was found to have hanged himself in his cell at 9.20pm local time (01.20am GMT).

Castro, 53, who was under protective custody in isolation from other inmates at the Correctional Reception Center in Orient, Ohio, was found by prison staff during their rounds at the facility, JoEllen Smith, Ohio Department of Rehabilitation and Correction spokeswoman, said.

Smith said that Castro 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," she said.

"Shortly after he was transported to OSUMC where he was pronounced dead at 10.52 pm.

"A thorough review of this incident is under way and more information can be provided as it becomes available pending the status of the investigation. "

Castro was sentenced to life in prison without parole, plus 1,000 years, on August 1 for holding Michelle Knight, Gina DeJesus and Amanda Berry captive in his home on Cleveland's west side.

He avoided the death penalty by pleading guilty to 937 charges during a trial in July this year, including aggravated murder for causing Knight to miscarry by beating and starving her.

Suicide note

Cuyahoga County prosecutor Tim McGinty acknowledged after Castro's sentencing that a suicide note and confession written by Castro was found by authorities at his residence when they searched his home after his arrest in May.

McGinty dismissed the letter as an attempt of Castro, whom he described as a "narcissist", to feel sorry for himself and to place blame on his victims.

Knight, 32, Berry, 27, and DeJesus, 23, went missing from the west side of Cleveland between 2002 and 2004. They were rescued on May 6, along with Berry's six-year-old-daughter by Castro, after neighbours heard Berry's cries and helped her break through the house's front door.

"I served 11 years of hell. Now your hell is just beginning," Knight said of Castro in a statement read to the court at his sentencing.

Knight was the oldest of the three victims, and was abducted when she was 20. Berry was 16 when she disappeared a few blocks from her home, and DeJesus was 14 when she disappeared while walking home from school on April 2, 2004. 

Police said the women had been held in separate rooms, but had known of the presence of the other women in the house.

Agencies