Craig Weinstraub. appearing Wednesday on NBC's "Today" show, said authorities twice denied his request for independent psychiatric evaluations of Castro, who was found hanged by a bed sheet in his cell Tuesday night at the Correctional Reception Center in Orient, Ohio, where he was serving a prison sentence of life plus 1,000 years after he pleaded guilty to the abductions, captivity and rape of Amanda Berry, Gina DeJesus and Michelle Knight.
Weintraub, told Cleveland.com Wednesday he asked the center's warden to allow a defense scientist to evaluate Castro, 53, but was denied two weeks before Castro's death.
A spokesman for the state Department of Correction and Rehabilitation couldn't confirm whether a request had been made.
"There's no doubt that he had psychological problems, and it's obvious, throughout the case, that's what this case was about -- somebody who was deeply disturbed," Weintraub said on "Today."
"We'll find out exactly what happened," he said.
"A thorough review of this incident is under way," Ohio Department of Rehabilitation and Correction spokeswoman JoEllen Smith said in a statement to NBC News.
"I'm going to be very interested to hear what they have to say about how in depth and what the wide scope of the independent evaluation was that they may have conducted," Weintraub said. "If it's anything but a suicide or it is a suicide, we're going to get to the bottom of it. There's no way we're going to let this go especially in light of the fact that it's been 30 days [since Castro began serving his sentence]."
He said his first request for an independent forensic evaluation, submitted while Castro was still being held at the county jail, and a second request after Castro was sent to the Lorain Correctional Institution were both denied.
Weintraub told Cleveland.com one reason he made the request was because of a letter the FBI found in Castro's Seymour Avenue home written in 2004, in which Castro referred to suicide.
"When taken with the pressures of being an inmate ... it's a recipe for disaster," Weintraub said.
John O'Brien, a spokesman for the Cuyahoga County Sheriff's Office, said Castro was placed on suicide watch and administrative segregation when he was taken into custody in May, routine treatment for high-profile inmates.
After he was evaluated by psychologists, Castro was downgraded to suicide precaution, O'Brien said.
"We felt he wasn't a danger to himself," O'Brien said.
He said Castro showed no signs of unusual behavior while he was in jail.
"We look for whether people either have trouble or are dealing with the situation," O'Brien said, adding that Castro "was dealing with the situation."
Castro, an unemployed bus driver, was sentenced Aug. 1 in a plea deal that let him avoid a possible death sentence.
He admitted to 937 criminal counts of rape, kidnapping and aggravated murder associated with the abduction, beating and restraining -- sometimes in chains -- of Berry, DeJesus and Knight. The three women disappeared separately between 2002 and 2004, when they were 14, 16 and 20 years old.
The women were rescued from Castro's house May 6 after neighbors spotted a frantic Berry and helped her break out.