The death in custody of Linton Ryan, a young Aboriginal man whose calls for help were allegedly ignored, was preventable and is an indictment on broader failings in the justice system, a leading human rights expert says.

Kurin Minang human rights expert and law academic Dr Hannah McGlade told National Indigenous Times the audio recording of a police officer laughing about Mr Ryan's death was "vile".

"Here we have a voice recording from a police officer that is shocking and revealing of the systemic racism in police in WA," she said.

"This is a very serious matter. Linton Ryan could be alive today if his health concerns were taken seriously.

"He was reaching out for help, but that was dismissed by an officer who laughed about his death when she learnt about it the following day. It is so vile. It is an act of racist violence."

On Monday, an ABC Regional Investigation published a voice message sent by a serving police officer days after Mr Ryan, 31, died in his cell at Eastern Goldfields Regional Prison on 2 April this year.

In the message, the officer admits she dismissed Mr Ryan's warning that he was going to take his own life.

She signed off the voice note with a laugh and the comment "um, lol", before sending a follow-up message: "don't tell anyone that".

WA Premier Roger Cook told reporters on Monday the alleged behaviour was "unacceptable".

"We want the police to be there to keep everyone safe and the way they do that is to exemplify the values of the West Australian police force," he said.

Opposition corrective services spokesperson Adam Hort said "the behaviour alleged against the officer, ignoring a suicide threat and then mocking the death of a man in custody, is completely unacceptable".

"The community expects the highest standards of our police officers, and while the vast majority do outstanding work, this alleged conduct is nowhere near those standards," he said.

WA Police said the constable has been stood aside following the ABC's enquiry, and an internal investigation is underway.

Mr Ryan, a Noongar Wongai Adnyamathanha man, was on remand at the time and charged with aggravated assault occasioning bodily harm.

Dr McGlade, a member of the United Nations Permanent Forum on Indigenous Issues, said the issue goes beyond one officer.

"I believe there are wider failings that are at play in this case, including the failure to properly implement the recommendations from the Royal Commission into Aboriginal Deaths in Custody," she told National Indigenous Times.

"This young man should not have been incarcerated; he should have been sent to the Aboriginal men's healing centre, where he could have gotten help rather than having his life put at risk.

"This was a preventable death. There are still hanging points throughout the prison system."

Data compiled by the Australian Institute of Criminology from the past 10 years for the ABC investigation revealed Western Australia has the worst rate of Indigenous deaths in custody, per capita for the state's Indigenous population, of any state or territory: as was the case according to the findings of the Royal Commission into Aboriginal Deaths in Custody which brought down its findings in 1991.

Dr McGlade noted that the WA government "re-established the Aboriginal Justice Committee, but they failed to ensure it is an independent, strong voice for Aboriginal people".

"The Royal Commission recommended state and federal Aboriginal justice committees to make sure its recommendations were implemented. That still has not happened three decades later," she said.