"These degenerate molesters are cowards," Cuyahoga County Prosecutor Timothy McGinty said in a statement. "They con and capture vulnerable children. This man couldn't take, for even a month, a small portion of what he had dished out for more than a decade."
"Let this be a message to other child kidnappers: There will be a heavy price to pay when you are caught," he said. "You won't enjoy the captive side of the bars."
Castro, 53, died after being found hanging in his cell at Correctional Reception Center in Orient, Ohio, Tuesday at 9:20 p.m. local time, Ohio Department of Corrections spokeswoman JoEllen Smith said.
Facility staff tried unsuccessfully to resuscitate the prisoner, according to Smith. Castro was taken to Ohio State University Medical Center and was pronounced dead at 10:52 p.m.
Autopsy results showed that the death was a suicide by hanging, Franklin County coroner Dr. Jan Gorniak told ABCNews.com today.
"The autopsy findings and the ligature that I was shown, it's consistent with a bed sheet," Gorniak said of the manner in which Castro committed suicide.
She did not know provide details of how he was found.
His room was an 8 by 12 cell with a bed, urinal, sink, shower stall and writing surface, according to the Ohio Department of Corrections. Inmates are also allowed to have some personal property if they are not on any type of disciplinary probation.
"Inmate Ariel Castro was found hanging in his cell this evening at 9:20 p.m. at the Correctional Reception Center in Orient. 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," Smith said in a statement.
Castro was not on a suicide watch, which would have required constant observation.
"A thorough review of this incident is underway and more information can be provided as it becomes available pending the status of the investigation," the statement concluded.
A public relations company that has represented Michelle Knight, Amanda Berry and Gina DeJesus said that Castro's former captives will not be commenting on the matter.
DeJesus' brother told ABC News that they are aware of Castro's death and are all doing okay so far.
Castro's attorney Jaye Schlachet told ABC News' Cleveland affiliate WEWS-TV that the defense team had requested for a forensic psychologist to evaluate Castro when he was in the county jail and the state's prison reception center.
"Local and state authorities denied our requests," Schlachet said in the statement. "There is an institutional failure beyond Ariel Castro and the citizens of Ohio are entitled to something better. It's just sad."
Cleveland Mayor Frank Jackson said focus should remain on the survivors.
"Our focus remains on the well-being of the survivors of Seymour Avenue," Jackson said. "It is our sincere hope that they will continue to heal and recover. I ask the community to continue to respect the privacy of the survivors so that they can move forward with their lives."
Castro was sentenced to life in prison without parole plus 1,000 years by an Ohio judge Aug. 1. Castro, a former school bus driver, kidnapped Knight, Berry and DeJesus between 2002 and 2004 and imprisoned them, sometimes restrained by chains, in his Cleveland home.
Castro pleaded guilty to 937 counts, including kidnapping, rape, assault and aggravated murder. The plea deal spared Castro the death penalty because he was accused of the aggravated murder of a fetus after forcibly causing an abortion in one of his victims that he is accused of impregnating.
The women escaped May 6, when Berry broke part of a door and yelled to neighbors for help. Castro was arrested that evening.
The home where Castro held his victims was torn down last month as part of the plea deal.
Castro was also watched closely in the Cuyahoga County Jail in the weeks after his arrest. He was taken off county jail suicide watch in early June after authorities determined he was not a suicide risk.
At Castro's sentencing hearing last month, he shocked a Cleveland court by saying he was "not a monster," "lived a normal life" and that the sex he had with the three women he held captive for more than a decade was "consensual."
Castro's statement came after Knight confronted him for the "hell" she endured in his house for 11 years.
Castro showed no reaction to the remarks by Knight. Instead, he gave a rambling speech in which he depicted himself as a person who had "everything going" for himself but was plagued by an addiction to porn.
During the hearing, detectives told how he captured the three women and subjected them to a decade of torture, which one woman wrote in a diary was like being held as a "prisoner of war."
While in captivity, Berry gave birth to her now 6-year-old daughter, who Castro fathered.