Professor Morgan said it previously cost about $500,000 a year for each youth in detention, but the figure was likely to have increased to about $1 million.

“We need to sit back and say, ‘how do we best spend that money?’ and that is probably a job that is best done by a standalone, small, focused department,” he said.

Professor Morgan also called for smaller regional youth detention centres and for detainees to be separated by age, so children were not mixed with older teens.

He said the Kimberley was as far from Perth as Russia was from the UK.

“It’s probably not much different in terms of culture [distance],” he said.

“Why do we think that will work?”

Prof Morgan also raised concerns over Casuarina Prison’s Unit 18, where Cleveland was held, which was set up as a temporary facility for young detainees three years ago.

“There has to be a closure date,” he said.

The unit was supposed to be open for one year from July 2022 after a riot at Banksia Hill damaged that facility.

The inquest continues on Tuesday, when the current inspector of custodial services, Eamon Ryan, is scheduled to give evidence.