Cleveland Dodd was found unresponsive inside a cell in a troubled 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 about one week later, causing outrage and grief in the community.
Former inspector of custodial services Neil Morgan said Western Australia's youth detention facilities had been in crisis for more than a decade and the justice department had forgotten it was dealing with children.
"We must treat children as children," he told a coroner on Monday.
"We should stop trying to demonise, blame and break them.
"Until that language stops I don't see how we can progress forward."
Cleveland Dodd was found unresponsive in his cell in the youth wing of Casuarina Prison in Perth. (Aaron Bunch/AAP PHOTOS)
Professor Morgan said it was "time for the department to stop breaking the law" following two Supreme Court rulings against it.
"There's been no sense that locking children up for upwards of 20 to 23 hours a day will somehow have a deleterious impact on them," he said.
Aboriginal Legal Service director Peter Collins told the court two weeks before Cleveland died, his office had requested the department transfer the teen from Unit 18 to Banksia Hill Youth Detention Centre but received no response.
The letter said conditions at Unit 18 were affecting Cleveland's wellbeing, he wasn't able to access education and was being locked in his cell for long periods.
Mr Collins said the department failed to reply to most of the service's letters, including one that raised concerns about the unit over frequent lockdowns, lack of access to education and inadequate mental health support and responses to serious harm.
He said the department transferred youth detainees to Unit 18 "under a cloak of secrecy" and it had failed to respond to questions about the closure of the unit, which was set up as a temporary facility.
Mr Collins said the facility was painted as a "silver bullet" to end the problems at Banksia Hill "but the reality couldn't be further from the truth".
He said detainees had been "demonised" as murderers and rapists and the facility wasn't therapeutic or rehabilitative as promised.
He said isolating vulnerable young Aboriginal detainees at the unit was damaging to their mental health.
"Connection to family, that social and familial interaction on a daily basis with your community underpins your entire existence," he said.
"To then be cast into a situation in Unit 18, on your own, in a cell for hours on end, with very limited out-of-cell time, confined ... with little or no interaction with other young people."
Cleveland's grandmother Glenda Mippy (left) spoke out after an officer was not required to appear. (Aaron Bunch/AAP PHOTOS)
Outside the court, Cleveland's family and supporters vented their frustration and anger after Coroner Philip Urquhart excused a key witness from giving evidence over fears for his mental health.
Unit 18's senior officer in charge the night the Cleveland self-harmed, Kyle Mead-Hunter, was found partially clothed in a darkened office by a lower-ranking officer after the teen was found in distress.
Cleveland's grandmother Glenda Mippy said she was disgusted.
"He was the one who was sleeping on the job ... we wanted to hear from him,'' she said.
The inquest continues on Tuesday.
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