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Mr. Cumaiyi, 31 and described as shy by relatives, was never prosecuted for domestic violence after his arrest. Nonetheless, nearly three years later, he is still in a Darwin prison after pleading guilty to other charges, including assaulting two officers and “endangering the safety of an aircraft.”

Now, Stewart Levitt, one of Australia’s most prominent lawyers, is demanding that Mr. Cumaiyi’s case be reconsidered. He lodged a complaint on Wednesday with the Australian Human Rights Commission, accusing the Australian government of human rights violations and negligence stemming from systemic racial discrimination.

Mr. Levitt said the evidence of a cover-up was clear: The official police account said nothing about the eyewitness reports that Mr. Cumaiyi was struck in the head with a flashlight and slammed onto the tarmac.

Instead, it suggests that he hurt himself the day after his arrest by jumping from a police van traveling at 50 miles, or about 80 kilometers, per hour — a claim that two medical experts dismissed as unlikely given his injuries, and that Mr. Levitt called “implausible, counterintuitive and not witnessed by anyone.”

The Northern Territory Police Force did not respond to requests for comment about the case.

Mr. Levitt, who won a large judgment last year for another Indigenous community confronting police mistreatment, said that “there seems to have been a determined effort to deflect all attention away from the police assaults.”

He added, “This is an example of the racial discrimination that’s so endemic.”