Calls have grown for a full and independent investigation of the death of a 24-year-old disabled Aboriginal man in police custody as the NT grapples with more claims of violence from police towards First Nations people.

The Warlpiri man with connections to the Yuendumu community died after being "taken to the ground" by two plainclothes on-duty officers at a Coles in Mparntwe/Alice Springs with a witness to the incident claiming the officer's "knee was behind his head".

The NT News reported on Thursday that court documents showed in 2020, the then 19-year-old was found unfit to stand trial due to mental impairment and was placed under a non-custodial supervision order.

On Wednesday evening, Warlpiri Elder Ned Jampijinpa Hargraves said the man who died was his jaja (grandson), who was living away from his community to receive help.

"This young man was living away from his community, in town, in supported accommodation because of his disabilities, and he was very vulnerable," Mr Hargraves said.

Police say they "restrained the adult male" after an altercation with a security guard at an Alice Springs Coles; however, the male "stopped breathing and CPR was commenced".

"St John Ambulance attended the scene, and the man was conveyed to Alice Springs Hospital, where he was pronounced deceased shortly after 2:20 pm," NT Police said.

NT Police have not explained how restraining somebody can lead to their death, what restraint they used, or what the meaning of "placed on the ground" means.

In a statement, the First Peoples Disability Network (FPDN) said the death in custody highlights the "increasing criminalisation of disability".

FPDN Chief Executive and Worimi man Damian Griffis said the "tragic event highlights the concerns we have been raising at FPDN for many years".

"It also exposes potentially serious failings with the Guardianship system and the NDIS," he said.

It was revealed on Wednesday that the NT's chief forensic pathologist had completed the autopsy of the man, finding the cause of death remains "undetermined".

As a result, the pathologist would conduct a "further investigation to provide any substantive cause of death," Assistant Commissioner Travis Wurst said.

The man is the eighth Indigenous person to die in custody this year and at least the 593rd to die in custody since the Royal Commission into Aboriginal Deaths in Custody brought down its findings - and issued over 300 recommendations - in 1991.

Not one person has been found guilty in connection to any of these deaths.

"How many more inquiries and funerals will it take before authorities act on the mountain of evidence we already have?" Mr Griffis said.

FPDN Chairperson Aunty Kay Sadler said the young man was evidently taking food from the store "because he was hungry, and being hungry is not a crime".

"Why was this young man hungry is the question, and why has he lost his life in police custody? This should be front-page news, and it should be a national outrage," she said.

Police have said the man was allegedly stealing food from the confectionary aisle, but have refused to address any of the actions of the police, citing the ongoing investigation.

"It is disgraceful that police are already putting out stories that portray my jaja as a criminal," Mr Hargraves said. "We are always told by lawyers that we need to wait for investigations to take place before we comment on events."

Speaking on ABC Radio on Thursday, Minister for Indigenous Australians Malarndirri McCarthy said it was "absolutely devastating news...to know that a 24-year-old man who was just searching for some food" had died.

"I've spoken to family members and expressed my sympathy, but also wanted to understand what they've been told, how they've been communicated with," she said.

"I've also reached out to the Chief Minister - who is also the Northern Territory Police Minister - to understand what the process is in terms of the investigation, but also to express my concerns given that this incredibly tragic incident has occurred when family members are also preparing for the handing down of the coronial inquiry into Kumanjayi Walker's death so many years ago."

Warlpiri-Luritja man Kumanjayi Walker was shot and killed in 2019 by former NT police officer Zachary Rolfe. Mr Rolfe was found not guilty on all charges in 2022.

The long-awaited findings into the inquest of Kumanjayi Walker, which has heard accounts of police racism and violence, are due to be handed down by Coroner Elisabeth Armitage on June 10 in Yuendumu.

However, Mr Hargraves has indicated he wants this to be postponed as the community is conducting Sorry business.

Assistant Commissioner Wurst has said the investigation would be led by a police commander from Darwin "to ensure it's done independently and transparently".

Mirroring other organisations and leaders, the FPDN called for an "immediate, fully transparent investigation led by an external body in partnership with the deceased man's family" and the immediate release of all body-worn camera and CCTV footage to the family "to ensure truth-telling and accountability".

"A young Aboriginal man with a disability has died yet again during an interaction with police. Our people are tired of condolences without consequence," Mr Griffis said.

"The Disability Royal Commission told governments exactly how to prevent these tragedies. Implementation has stalled, and our communities pay with their lives."

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