An unarmed black man died in New York state after he was hooded by police and held face down to the road for two minutes, body camera footage shows.
Daniel Prude, 41, was suffering from mental health issues when police restrained him in March.
He died in hospital a week later, but the news has only now become public as his family held a news conference.
Mr Prude’s death took place two months before the killing of George Floyd sparked global outrage.
Mr Prude’s brother, Joe, called police in Rochester, New York, on 23 March as his sibling was suffering from acute mental health problems.
“I placed a phone call for my brother to get help, not for my brother to get lynched,” he told Wednesday’s news conference.
“What is their sentence? You killed a defenceless black man. A father’s son, a brother’s brother, a nephew’s uncle.”
A warehouse worker from Chicago and father of five, Mr Prude was visiting his brother at the time of his death.
Police body camera footage obtained through a public records request shows Mr Prude, who had been running naked through the streets in a light snow before police arrived, lying unarmed as officers restrain him on the ground.
The video shows that Mr Prude complied immediately when officers arrived on the scene, ordering him to lie on the ground and put his hands behind his back. He is heard to say: “Sure thing, sure thing.”
He becomes agitated, at times swearing at the officers who surround him and spitting, but he does not appear to offer any physical resistance, according to the footage.
Mr Prude told officers he was infected with coronavirus, and they placed a “spit hood” over his head, which is meant to protect police from suspects’ saliva.
One officer is seen pressing down with both hands on Mr Prude’s head and saying: “Stop spitting.”
After he stops writhing and goes quiet, one officer notes: “He feels pretty cold.”
Medics try to revive him before he is carried into an ambulance. He was taken off life support a week later on 30 March.
The family’s lawyer said the reason the case was not made public earlier was that it had taken “months” for police footage to be released.
In a statement, New York state’s attorney general called the death a “tragedy” and said an investigation was under way. The officers involved have not been suspended.
According to a post-mortem examination report seen by the Rochester-based Democrat and Chronicle newspaper, Mr Prude’s death was a homicide caused by “complications of asphyxia in the setting of physical restraint”.
The report also listed PCP, a strong hallucinogenic drug, as a complication.
According to the newspaper, Rochester police used pepper spray and pepper balls against protesters on Wednesday outside the Public Safety Building.