Video of March encounter shows police put hood on Daniel Prude and pinned him down to the pavement for two minutes.

A Black man died of suffocation in Rochester, United States, in March after a group of police officers put a hood over his head and then pressed his face into the pavement for two minutes, according to video and records released by the man's family.

Daniel Prude died on March 30, after he was taken off life support, seven days after the encounter with police in Rochester, New York state.

His death did not receive public attention until Wednesday when his family held a news conference and released police body camera video and written reports they obtained through a public records request.

Prude's brother, Joe, said he called 911 on March 23 after his sibling, who was visiting from Chicago, ran out of their home in an erratic state.

Just the day before, Rochester police had taken Daniel Prude into custody for a mental health evaluation after he reported suicidal thoughts.

"I placed a phone call for my brother to get help. Not for my brother to get lynched," Joe Prude said at a news conference.

"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?"

'Trying to kill me'

The videos show Prude, who had taken off his clothes, complying when police ask him to get on the ground and put his hands behind his back. Prude is agitated and shouting as he sits on the pavement in handcuffs for a few moments as a light snow falls. "Give me your gun, I need it," he shouts.

Then, they put a white "spit hood" over his head, a device intended to protect officers from a detainee's saliva. At the time, New York was in the early days of the coronavirus pandemic.

Prude demands they remove it.

Then the officers slam Prude's head into the street. One officer, who is white, holds his head down against the pavement with both hands, saying "calm down" and "stop spitting". Another officer places a knee on his back.

"Trying to kill me!" Prude says, his voice becoming muffled and anguished under the hood.

"OK, stop. I need it. I need it," the prone man begs before his shouts turn to whimpers and grunts.

The officers appear to become concerned after he stops moving, falls silent and they notice water coming out of Prude's mouth.

"My man. You puking?" one says.

One officer notes that he's been out, naked, in the street for some time. Another remarks, "He feels pretty cold."

His head had been held down by an officer for just over two minutes, the video shows.

The officers then remove the hood and his handcuffs and medics can then be seen performing CPR before he is loaded into an ambulance.

A medical examiner concluded that 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.

Protests

The death is now under investigation by the New York State Attorney General's Office.

It occurred two months before the police killing of George Floyd, an unarmed Black man who died on May 25 after a policeman knelt on his neck for nearly nine minutes.

The Minneapolis death set off mass protests across the US and the world, with tens of thousands of demonstrators rallying against racial injustice and police brutality.

Rochester activists on Wednesday demanded that the police involved in 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 de-escalate.

"These officers are trained to ridicule, instead of supporting Mr Daniel Prude," Ashley Gantt of Free the People ROC said at the news conference with Prude's family.

Later in the day, dozens of protesters gathered outside Rochester's Public Safety Building, which serves as police headquarters, chanting: "Which side are you on?"

Free the People ROC said several of its organisers were briefly taken into custody after they entered the building while Mayor Lovely Warren was speaking to the media.

The mayor described the video showing Prude's restraint by police as "disturbing".

"I want everyone to understand that at no point in time did we feel that this was something that we wanted not to disclose," she told reporters.

"Rest assured that we are going to do everything possible to make sure that the truth comes out and that justice is held here," she added.