Cleveland Dodd was found unresponsive inside a cell in the youth wing of a high-security adult prison in the early hours of October 12, 2023.
The 16-year-old was taken to hospital in a critical condition and died a week later, causing outrage and grief in the community.
A Perth inquest into his death was told in the 12 days before he harmed himself, Cleveland spent between one hour and one hour and 55 minutes out of his cell per day.
Most days it was just one hour and 15 minutes outside his damaged and unfurnished cell in Casuarina Prison's Unit 18.
"It is cruel, inhuman and degrading that amount of time out," former Department of Justice director general Adam Tomison conceded from the witness box on Monday.
Cleveland Dodd died after self-harming in a youth detention centre in Perth. (HANDOUT/SUPPLIED)
Dr Tomison agreed the other 13 children and youths held in the unit in the last months of Cleveland's life were also subjected to cruel, inhuman and degrading treatment.
Cleveland's threats to self-harm on October 11 and 12 started after his fifth request for water was ignored.
He had covered a CCTV camera in his cell with tissue paper, blocking the view of correctional staff monitoring him from a control room, but it wasn't uncovered until they were fighting to save his life.
Asked about the decision to deny Cleveland's requests for water, Dr Tomison said: "It's appalling".
"I don't understand why it would occur full stop ... particularly given a number of the officers that were involved on the night that Cleveland hurt himself seem to have generally cared for young people."
The inquest has heard the justice department told the then corrections minister, stakeholders and detainee's families Unit 18 would have a full suite of services, including therapeutic programs, cultural support, health services, education and recreation.
In reality, it had few of these and detainees were held in damaged cells that in some cases didn't have running water.
The youth detainees sent to the unit were given little notice about the move, with Dr Tomison telling the inquest those selected were deemed disruptive.
"No one wanted to do it. It wasn't our first choice of action," he said.
"We did think it would actually enable us to work better with the young people at 18 ... we were at the point where we had to do something because the site at Banksia was just not functioning well."
Dr Tomison said the department believed the youth detainees sent to Unit 18 would be "better off" and they were told that if their behaviour improved they would be returned to Banksia Hill.
Staff shortages have been an ongoing issue for the department, with Dr Tomison agreeing the situation was dire by 2023.
When Cleveland died, only 56 and 58 per cent of senior officer and unit manager roles were filled respectively and 31 per cent of youth custodial positions were vacant.
The inquest continues.
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