A black man died of asphyxiation after a group of US police officers put a hood over his head then pressed his face into the pavement for two minutes.
Daniel Prude died in hospital on March 30 after he was taken off life support following his encounter with police in Rochester, New York.
Officers were called to help Mr Prude by his brother, who was worried about his welfare and mental health.
His death received no public attention until Wednesday, when his family held a press conference and released police body camera video and written reports they obtained through a public records request.
The videos show Mr Prude, who had taken off his clothes, complying when police ask him to get on the ground and put his hands behind his back.
He is agitated and shouting as officers let him writhe as he sits on the pavement in handcuffs for a few moments.
Joe Prude, Daniel’s brother, said: “I placed a phone call for my brother to get help. Not for my brother to get lynched.
“How did you see him and not directly say, ‘The man is defenceless, buck naked on the ground. He’s cuffed up already. Come on’.
“How many more brothers gotta die for society to understand that this needs to stop?”
The officers are seen putting a spit hood over Mr Prude’s head despite objections, with the victim saying: “Trying to kill me”.
These officers are trained to kill, and not to deescalate. These officers are trained to ridicule, instead of supporting Mr. Daniel Prude
The officers slam Mr Prude’s head into the street, then one officer holds his head down against the pavement with both hands, saying “stop spitting” as Mr Prude’s shouts turn to whimpers and grunts.
The officers appear to become concerned when they notice water coming out of Mr Prude’s mouth and paramedics were called.
A medical examiner concluded that Mr Prude’s death was a homicide caused by “complications of asphyxia in the setting of physical restraint”.
The report lists excited delirium and acute intoxication by phencyclidine, or PCP, as contributing factors.
Rochester police officers took Mr Prude into custody for a mental health evaluation around 7pm on March 22 for suicidal thoughts – around eight hours before the encounter that led to his death.
But his brother said he was only at the hospital for a few hours, according to the reports.
Police responded again after Joe Prude called 911 at about 3am to report that his brother had left his house.
One officer wrote that they put the hood on Mr Prude because he was spitting continuously in the direction of officers and they were concerned about coronavirus.
But activists demanded officers involved with Mr Prude’s death be prosecuted on murder charges and that they be removed from the department while the investigation proceeds.
“The police have shown us over and over again that they are not equipped to handle individuals with mental health concerns. These officers are trained to kill, and not to deescalate. These officers are trained to ridicule, instead of supporting Mr. Daniel Prude,” Ashley Gantt of Free the People ROC said.
Mr Prude, known to his Chicago-based family by the nickname Rell, was a father of five and had been working at a warehouse within the last year, said his aunt Letoria Moore.
“He was just a bright, loving person, just family-oriented, always there for us when we needed him,” she said.