Footage of a traffic stop that has seen five ex-Memphis police officers charged with murder shows them kicking and punching a motorist for several minutes as he cries out for his mother.
Officers are seen beating Tyre Nichols, 29, in the videos from the 7 January arrest, with no signs of him resisting.
US President Joe Biden said he was “deeply pained” by the “horrific” clip.
Lawyers for Mr Nichols’ family likened the assault to the 1991 police beating of Los Angeles motorist Rodney King.
Peaceful protests took place in Memphis on Friday night after the video was released, with some demonstrators blocking a major highway in the city, while small-scale demonstrations were held elsewhere in the country.
The first clip shows officers pulling Mr Nichols out of his vehicle and shouting at him to get on the ground.
“I didn’t do anything!” he says. Officers demand that he lie down flat.
“Get on the [expletive] ground!” one officer shouts, as another is heard saying: “Tase him!”
An officer shouts: “Put your hands behind your back before I break your [expletive].”
“You guys are really doing a lot right now,” Mr Nichols says to the officers. “I’m just trying to go home.”
Within seconds one of the officers fires a Taser at Mr Nichols, who leaps up and manages to run away.
A separate video, from a CCTV camera mounted on a utility pole, shows officers beating Mr Nichols after catching up with him in a residential area.
Two officers are seen holding Mr Nichols down while others take turns kicking and punching him and striking him with an expandable baton.
They drag him across the ground and prop him sitting up against a squad car. More than 20 minutes elapse until an ambulance is seen arriving.
The third and fourth videos show police body camera footage of the beating, with Mr Nichols being held down, pepper-sprayed and assaulted as he repeatedly shouts: “Mom!”
The videos also show officers milling about recounting details of the incident as Mr Nichols lies slumped against the car.
Some of them claim Mr Nichols “swung” at them or reached for their guns, though neither allegation is clear from the released video.
Officers can also be heard saying that nothing was found in his car.
Mr Nichols’ mother, RowVaughn Wells, has said her son was only about 230ft (70m) from home when Memphis police officers “murdered him”.
Representatives of the family have described Mr Nichols as the father of a four-year-old son and a keen skateboarder who had recently enrolled in a photography class. He worked for the FedEx parcel delivery firm.
One of the lawyers, Antonio Romanucci, said: “This young man, by definition of the law in this state, was terrorised.”
The video is “appalling”, Greg Donaldson, a professor at John Jay College of Criminal Justice in New York, told the BBC.
He said the lack of training stands out, with the police officers’ anger seeming to grow “as their incompetence seems to be more revealed”.
“The worse part of it was the inhumanity after the incident,” he added, as officers leave Mr Nichols “laying there on the ground like a piece of garbage.”
The five officers – Tadarrius Bean, Demetrius Haley, Desmond Mills Jr, Emmitt Martin III and Justin Smith – were fired last week.
They were taken into custody on Thursday and each faces charges of second-degree murder, aggravated assault, aggravated kidnapping, official misconduct and official oppression.
Four of the five posted bail and were released from custody by Friday morning, according to jail records.
Lawyers for Mr Martin and Mr Mills have said their clients will plead not guilty.
Memphis Police Director Cerelyn Davis described the five officers’ actions as “heinous, reckless and inhumane”.
With protests anticipated, she told US media that local officials had decided to release the video on Friday evening so that schoolchildren and commuters would have time to get home.
Reverend Al Sharpton, who will deliver the eulogy for Mr Nichols on Wednesday, asked protesters to “remain non-violent”, saying unrest would only help the defendants.
In a tweet the civil rights leader said the “sad reality” was police brutality would be “an ever-present threat for Black and Brown Americans unless cops continually see that those who use blunt force will go to jail”.
The protests around the country have so far been largely peaceful, which Mr Nichols’ family had called for, saying they didn’t “want any type of disturbance”.
One protester at the Memphis rally, 21-year-old Kyrion, told the BBC he had dreamed as a child of joining the city’s police force, but now that dream was shattered.”It’s just wicked, the system is forever going to be wicked,” he said. “Which is why I’m out here today, as of right now I can’t count on [police] to protect me.
“How do I know the man is not going to put his knee into my neck, or hold me down and beat me into a pulp?”
After the videos were released, Shelby County Sheriff’s Office said two of its deputies had also been relieved from duty pending an investigation into their conduct.