COLUMBUS, Ohio -- The man who kidnapped three young women and repeatedly raped them in his Ohio home for nearly a decade hanged himself in his cell, prison officials said Wednesday.

Ariel Castro, 53, last month was sentenced to life in prison plus 1,000 years after his guilty plea in one of the most sensational criminal cases in recent U.S. history. The public was startled by his apparent double life, with his reputation as a good-natured musician who even attended a vigil for one of the missing women.

Castro was found Tuesday night, said JoEllen Smith, Department of Rehabilitation and Correction spokeswoman. Prison medical staff performed CPR before he was transported to a hospital, where he was pronounced dead. He had used a bedsheet.

Castro had been in protective custody because of the notoriety of his case, meaning he was checked every 30 minutes, but he was not on suicide watch, Smith said. She said suicide watch entails constant observation. While in jail before his conviction, Castro was taken off suicide watch in June after authorities determined he was not a risk.

An autopsy showed the death was a suicide, said Dr. Jan Gorniak, a coroner. She said she couldn't comment on the circumstances in which Castro was found.

The American Civil Liberties Union of Ohio asked the prison system to conduct a full investigation.

State Prison Director Gary Mohr lordered a review of Castro's medical and mental health treatment and the circumstances surrounding his suicide. He said the state police were also investigating.

No one answered the door Wednesday morning at the home of Castro's mother and brother.

Cuyahoga County Prosecutor Tim McGinty said in a statement Wednesday: "This man couldn't take, for even a month, a small portion of what he had dished out for more than a decade."

Through a spokeswoman, the three women declined to comment.

At his sentencing, Castro told the judge he was suffering from a pornography addiction.

"I'm not a monster. I'm sick," he said.

The three women disappeared separately between 2002 and 2004, when they were 14, 16 and 20 years old. They escaped from Castro's home May 6, when Amanda Berry, one of the women, broke part of a door and yelled to neighbours for help.

The two other women were so scared of Castro that they held back even as police officers began to swarm the house. But quickly they realized they were free.

"You saved us! You saved us!" Michelle Knight told an officer as she leaped into his arms.

Castro was arrested that evening. He had fathered a child with Berry while she was in captivity; that girl was 6 years old when freed.

A judge rejected Castro's request to have visiting rights with his daughter.

Investigators said the women had been bound with chains, repeatedly raped and deprived of food and bathroom facilities. Knight told investigators she was beaten and starved several times to force her to miscarry. Berry was forced to give birth in a plastic kiddie pool.

Castro's attorneys had tried unsuccessfully to have a psychological examination of him done at the jail before he was turned over to state authorities following his conviction, his attorney, Jaye Schlachet, told The Associated Press early Wednesday. Schlachet said he could not immediately comment further.

In an interview last month after Castro's conviction, his attorneys said their client clearly fit the profile of sociopathic disorder and that they hoped researchers would study him for clues that could be used to stop other predators.

The prison where Castro had been placed holds nearly twice as many prisoners as the 900 it was meant to hold, according to state data.

Stress is high and assaults are up at the prison, but Tim Shafer, an official with the prison guards' union, said: "Just like out in the public, suicides happen, and you just can't prevent every one of them."

Residents of the neighbourhood where the women had been held expressed mixed feelings Wednesday, from sadness to anger that Castro did not serve the prison time he deserved to serve.

"We're sad to hear that he's dead, but at the same time, we're happy he's gone," said Elsie Cintron, a neighbour who lived up the street from him.

Only one of the three women appeared in court at Castro's sentencing.

"I spent 11 years in hell," Knight said. "Now your hell is just beginning."