More than 100 experts, organisations and notable Australians have written to the Western Australian Premier to urge the closure of the state's notorious Unit 18 youth jail.

The open letter was sent to Roger Cook on Friday, the final day of the first part of the inquest into the death of Cleveland Dodd, the 16-year-old Yamatji boy who died in the notorious Unit in October.

The 127 signatories included former WA Premier Peter Dowding, Indigenous human rights law expert Dr Hannah McGlade, Dr Fiona Stanley, ALS WA chief executive Wayne Nannup, former Children's Court president Denis Reynolds, Danny Ford, and Commissioner Jacqueline McGowan Jones, along with representatives signing on behalf of Community Legal WA, Consumers of Mental Health WA, Palmerston, the National Justice Project, YIC, Ebeneezer, Vinnies WA, Samaritans, Yorugm, Anglicare, Yorganop, Human Rights Law Centre, Aboriginal Health Council of Western Australia, Ruah, Reconciliation WA, and many more.

The letter was coordinated by Social Reinvestment WA.

The organisation's Principal Manager, Sophie Stewart, said WA's first death of a child in prison custody "should matter to every West Australian".

"This Inquest has exposed institutional abuse of children occurring right here in a Perth suburb. We've seen frankly astonishing testimony where public servants admit to serious lies, and law breaking," she said.

"Cleveland and his family were horrifically failed by the WA Government.

"The WA government has failed every child who has been subjected to cruel, unusual, and degrading treatment inside Banksia Hill and Unit 18."

Ms Stewart said the WA government has failed "every Western Australian citizen who expects government to act with decency and integrity on our behalf, especially when it comes to children in their care".

"Experts are unequivocal that Unit 18 needs to close - and now," she said.

"We need to transform our states youth justice system. Solutions like Social Reinvestment WA's Blueprint for a Better Future are lying there, ready and waiting to be used.

"We can make sure this never happens again."

The letter:

"Dear Premier Cook,

We represent leaders and experts from across the state.

The evidence revealed in the Coronial Inquest into the death of 16-year-old Cleveland Dodd inside Unit 18 has been both astonishing and damning. It has exposed massive failings in the management of youth detention.

It has been revealed that Unit 18 was never able to provide children the support they needed. Instead, these young people were locked down for more than 22 hours a day, in filthy cells with soiled clothes. And the public servants who oversaw it's opening knew it would be unable to provide basic care, including observation cells, access to services, and education.

The government was warned by WA's own prison inspector as far back as 2021 that they were breaching human rights conventions. That conditions inside detention amounted to 'cruel, inhuman, and degrading' forms of punishment.

The former Director-General of Justice gave testimony that conditions in WA's youth detention facilities were a form of 'institutional abuse of children.'

Senior public servants admitted Unit 18 was founded on 'a series of grievous lies.' Lies that Unit 18 would or could be safe. Lies that were told to the Minister, to the children, to the families, and to the public. But Unit 18 wasn't safe. It never could be. And in October 2023, a child inside Unit 18 took his own life.

The practice of keeping WA children inside a maximum-security adult prison must stop. The cycle of abuse and irreparable harm to children in government institutions must stop.

WA's youth justice system is a stain upon the character of our state. We call on you to heed the words of Coroner Urquhart and close Unit 18 as a matter of urgency, immediately.

We call on you to commit to a transformation and overhaul of the entire youth justice system, which is failing on every possible measure.

We stand in support of the proven solutions like Social Reinvestment WA's Blueprint for a Better Future.

Experts have been advocating for evidence-based and practical solutions transform our youth justice system into one that works. The abuse of children in state government institutions should not be politicised. The lives of young people should not be politicised.

Closing Unit 18 and investing in evidence-based alternatives across our youth justice system is an investment in community safety. In children's wellbeing. In future health and mental health. For generations to come.

We call on you Premier, to right this wrong. We ask you to act now to end the abuse of children happening on your watch, at the hands of your government, in a suburb of our capital city. Your government has the power to change this story.

To save more young people from a fate like Cleveland's."

National Indigenous Times has contacted the office of the Premier for comment.