A white US police officer has been charged with murder after shooting dead a black driver during a traffic stop over a missing car licence plate.
University of Cincinnati police officer Ray Tensing killed 43-year-old Samuel Dubose after pulling him over near the campus on 19 July.
"He purposely killed him," prosecutor Joe Deters said. "He should have never been a police officer."
The issue of excessive police force has sparked national debate and protests.
Video released on Wednesday appears to contradict Officer Tensing's police report, which said he was "dragged" by DuBose's car as he drove away and fired a shot, hitting him in the head.
Mr Deters called it the "most asinine act" by a police officer he had ever seen.
The video shows the two having a friendly exchange with tensions escalating only shortly before the violence.
The officer asks for DuBose's driver's licence and he says he does not have it but he is not suspended from driving.
DuBose shows the officer an unopened bottle of liquor in the car.
Officer Tensing then asks DuBose to unbuckle his seatbelt. Almost immediately after that, a shot is fired and the car appears to move.
Local media reports said Officer Tensing had turned himself in to law enforcement.
DuBose's death follows a series of cases in which black people have died in police custody or during arrest.
In recent week protests have focused on Sandra Bland, a black woman who was arrested after a traffic stop but later found dead in her Texas jail cell.
Cincinnati Mayor John Cranley said protestors have every right to be angry and that the city police department is "ready to deal with anything happening".
Mayor Cranley said he respects the right of people to peacefully protest DuBose's death.
"We wanted the just, fair thing to be done, we wanted the truth to come out," Mayor Cranley said.
He said the county prosecutor, in indicting Officer Tensing, was "not pushing an agenda, but doing the right thing".
Terina Allen, DuBose's sister, said her brother was not a "thug in the neighbourhood", had no gun and did not harm the officer.
The charges are some sort of justice for her brother, she said.
"We knew the video was going to vindicate our brother."