Courtesy NBC News

By Alexander Smith, NBC News contributor

Two investigations were launched late Wednesday into how kidnapper and rapist Ariel Castro managed to hang himself with a bedsheet while in protective custody.

Gary Mohr, director of the Ohio Department of Rehabilitation and Correction, said one review would look at the suicide itself while the other would assess Castro's circumstances and care in the days leading to his death, The Associated Press reported.

The 53-year-old former bus driver was sentenced to life plus 1,000 years after pleading guilty to 937 counts including rape, kidnap and aggravated murder following the decade-long incarceration of Amanda Berry, Gina DeJesus and Michelle Knight at his Cleveland home. Castro was found hanging in his cell late Tuesday -- just a month into this term.

Authorities found a suicide note at his house following his arrest in May, Cuyahoga County prosecutor Tim McGinty said after Castro's sentencing. According to Castro's attorney Craig Weintraub, his client was initially placed on suicide watch while in jail but this was later downgraded.

When he was transferred to the Correctional Reception Center in Orient, Ohio, he was put in protective custody, a common measure for prisoners who are at risk from other inmates. This meant he was in a cell on his own and checked every 30 minutes.

Franklin County Coroner Jan Gorniak said Wednesday the cause of death was suicide by hanging and the injuries were consistent with someone using a bedsheet.

Speaking on NBC's TODAY, Weintraub vowed to get to the bottom of the circumstances surrounding Casto's death.

"We'll find out exactly what happened," he said. "There's no way we are going to let this go."

The American Civil Liberties Union of Ohio also called for a thorough investigation into the incident.

"As horrifying as Mr. Castro's crimes may be, the state has a responsibility to ensure his safety from himself and others," said ACLU of Ohio executive director Christine Link. "Questions remain whether Mr. Castro was properly screened for suicide risk and mental illness. Prisons officials must address these issues, not only to fully account for how Mr. Castro was able to commit suicide, but also to prevent this from occurring again."

Earlier, an expert on preventing prison suicides told NBC News that authorities should "be very careful and take as much time as possible to look at both the inmate and the prison system to see if it did its due diligence."

"I would not be surprised if there is a quick investigation and determination that this was not a preventable suicide,"said Lindsay Hayes, project director at the National Center on Institutions and Alternatives.

Some of Castro's former neighbors did not mourn him Wednesday.

Elsie Cintron, who lived up the street from the former school bus driver, said: "We're sad to hear that he's dead, but at the same time, we're happy he's gone, and now we know he can't ask for an appeal."

Carina Hughes, 34, who lives a couple blocks away, decided to come visit the spot where the women had been held after hearing Castro was dead.

"I just needed to be here. I just relate to the girls," she said. "It could have been me. It could have been my daughter."

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