The inquest into the death of Yamatji 16-year-old Cleveland Dodd, WA's first recorded death in youth detention, has become a flashpoint this week for a legal battle over the scope of the Coroner's powers and the accuracy of Justice Department data.

The coroner's inquiry is examining Cleveland's death in 2023, which occurred a week after he self-harmed in Unit 18, the controversial youth detention facility set up within Casuarina Prison, a maximum security adult jail.

The Justice Department's submission of evidence has been met with criticism after a report by former Children's Court president Denis Reynolds and ex-custodial services inspector Neil Morgan challenged the department's figures.

Professor Morgan initially told the inquest that approximately 20 per cent of young detainees had passed through Unit 18. The department later countered this with a figure of 5.8 per cent, sparking a dispute.

Coroner Philip Urquhart expressed frustration, suggesting that the department's stance seemed to avoid a deeper investigation into why young people were placed in such a facility.

During the hearings Mr Urquhart said "It looks like the department doesn't want an exploration of this particular issue", the ABC reports.

Further complicating the inquest is the department's effort to limit the scope of the inquiry. Lawyers for the department argue the coroner should focus only on the immediate circumstances of Cleveland's death, not the broader systemic issues related to Unit 18's creation or operation.

This narrow interpretation of the Coroner's Act, if accepted, could exclude crucial evidence about the conditions in the facility, which staff have described as inhumane. The facility has reported an alarming rate of self harm.

Coroner Urquhart voiced concerns that adopting a limited view would nullify the court's ability to make meaningful recommendations, calling the department's interpretation "a stab in the dark."

As the inquest continues, these legal battles will likely shape its outcome, highlighting broader issues about transparency and accountability within WA's juvenile justice system.