An unarmed African-American died in New York state after the police held him down on the road for two minutes and also put a "spit hood" on his head, designed to protect officers from a detainee's saliva, according to body camera footage.
Although the incident took place in March, it came to light only on Wednesday, the BBC reported.
In a news conference on Wednesday, the brother of the victim, Daniel Prude, 41, said he called police in Rochester, New York, on March 23 as the latter 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," the BBC report quoted Joe Prude as saying.
A warehouse worker from Chicago and father of five, Daniel Prude was visiting his brother at the time of his death.
Police body camera footage obtained by the family showed the victim, who had been running naked through the streets in a light snow before police arrived, lying unarmed as officers restrain him on the ground.
In the video, Daniel Prude is seen to comply immediately when officers arrived on the scene and ordered him to lie on the ground and put his hands behind his back.
Once he was restrained, the victim told officers that he was infected with coronavirus, and they placed a "spit hood" over his head.
"Spit hoods" are mesh fabric hoods placed over the heads of suspects to prevent spitting or biting.
One officer is seen pressing down with both hands on his head and saying: "Stop spitting."
After he stops writhing and goes quiet, one officer can be heard saying: "He feels pretty cold."
Medics try to revive him before he is carried into an ambulance. He was taken off life support on March 30.
Protesters gathered in the city of Rochester, New York, on Wednesday to condemn Daniel Prude's death, the BBC reported.
In a statement, the New York state's attorney general called the death a "tragedy" and said an investigation was underway.
The officers involved have not been suspended.
Daniel Prude's death took place two months before George Floyd, also an unarmed African-American man ,died on May 25 in Minneapolis after a white police officer knelt on his nect for some nine minutes.
Floyd's death triggered protests against police brutality and racism across the US and also the world.
Tensions have escalated in the US again after 29-year-old Jacob Blake was shot seven times in the back by a white policeman in Kenosha, Wisconsin on August 23.
The cause of Blake's shooting remains under investigation.