In short:

Tim Marney, who was hired to overhaul WA's youth justice system, has told a coronial inquest the culture in youth detention was "dysfunctionally toxic".

He told the coronial inquest into the death of a 16-year-old in youth detention the extent of the inadequacies became clearer the closer he got to staff on the ground.

What's next:

The inquest continues.

The man who had been tasked with overhauling WA's troubled youth justice system has told a coronial inquest a "dysfunctionally toxic" culture was the root cause of all problems behind bars.

WARNING: This story discusses incidents of self-harm and contains the name and image of an Indigenous person who has died.

Coroner Philip Urquhart today embarked on a fourth round of hearings into the death of Cleveland Dodd, the state's first in youth detention.

The 16-year-old died in October last year after self-harming inside his cell in Unit 18, a youth detention facility hastily set up inside the adult, maximum security Casuarina Prison in mid-2022.

The coroner today heard from Tim Marney, the state's former under treasurer and mental health commissioner who in 2022 developed a new way of running the then-only youth detention centre at Banksia Hill Detention Centre.

In March 2023 he took up a job in the Justice Department implementing that plan, with then-minister Bill Johnston saying he was "ideally suited to tackling the challenges in youth detention".

But there was uproar later that year when his six-month contract was not extended as expected.

'Toxicity of culture'

Reflecting on his time working both with the department as a consultant and within the walls of Banksia Hill, Mr Marney told the court there was "a cluster, I guess, of toxicity of culture".

"There was a breakdown in the quality of the relationship from [department] leadership to … management to operational staff," he told the court.

"To the extent that the culture, which is a summary term for the way in which they interact and deal with each other, was dysfunctionally toxic."

Mr Marney described "the extent of the dysfunction and the toxicity" becoming clearer the closer he got to staff on the ground as he began implementing the plans.

"By six weeks in it was very clear that that was the root cause of all issues … [including] behaviour among youth detainees," he said.

Within weeks, in May 2023, Banksia Hill saw one of its worst ever riots with then-premier Mark McGowan likening the actions of detainees to terrorists as they caused more than $20 million of damage.

Mr Marney said the dysfunction stemmed from a lack of commitment to change, poor communication, "poor behaviours" and a "distinct lack of consistency" around what acceptable behaviour for staff and young people looked like.

Mr Marney told the court as time went on, he noticed more resistance, which he described as "passive aggressive."

"I was receiving feedback that hadn't been provided to others from operational staff, from young people, that painted senior management and leadership in a very bad light," he said.

Department not interested

Mr Marney agreed with counsel assisting the coroner Anthony Crocker's suggestion that the lack of commitment to change started at the top, with then-Director General Adam Tomison.

"Shit flows down from there, basically," Mr Marney said.

Mr Marney became emotional while speaking about the commitment the "vast majority" of youth custodial officers had to their jobs, saying: "They gave them love and support and they gave them what they needed from a therapeutic approach, they treated them as humans."

But he said issues arose during the reform process, which sought to empower officers and to take away power from senior management.

Additionally, "there was a fundamental misalignment between the authority that I had and what I was asked to achieve".

Mr Marney recalled communications with Roger Cook and his staff, both while he was Deputy Premier and after he took on the top job, as well as former minister Bill Johnston and his successor Paul Papalia about those issues, particularly with accessing staff for training and getting young people into programs.

"They were being fed bullshit," he claimed, saying he believed each politician was committed to improving youth detention but what the department told them did not line up with his experiences on the ground.

Lawyer Grant Donaldson SC, representing former deputy commissioner for women and young people Christine Ginbey, later produced a briefing note she sent to Mr Johnston highlighting some of Mr Marney’s concerns.

Attempt to restrict evidence

Earlier in the hearing, the Department of Justice failed in another bid to restrict the evidence heard by the inquest.

Late last night, the department's lawyers filed 10 pages of submissions arguing certain documents and evidence from four witnesses, including Mr Marney, were not relevant.

The argument was quickly rejected by Coroner Philip Urquhart, who said if he accepted what the department was saying he would not be able to investigate the systemic failings which may have contributed to Cleveland's death.

The inquest continues.