The death of Rayshard Brooks, a black man killed by a white police officer in Atlanta, was a homicide caused by gunshot wounds to the back, the Fulton County Medical Examiner’s office says.

Mr Brooks’ death on Friday reignited protests in Atlanta after days of worldwide demonstrations against racism and police brutality prompted by the death of George Floyd, 46, an African American, in Minneapolis police custody on May 25.

An autopsy conducted on Sunday showed that Mr Brooks, 27, died from blood loss and organ injuries caused by two gunshot wounds, an investigator for the medical examiner said in a statement.

The manner of his death was homicide, the statement said.

Mr Brooks’ fatal encounter with police came after an employee of a Wendy’s restaurant in Atlanta phoned authorities to say that someone had fallen asleep in his car in the restaurant’s drive-through lane.

Caught on the officer’s body camera and a surveillance camera, the encounter seemed friendly at first, as Mr Brooks cooperated with a sobriety test and talked about his daughter’s birthday.

“I watched the interaction with Mr Brooks and it broke my heart,” Atlanta Mayor Keisha Lance Bottoms said on CNN.

“This was not confrontational. This was a guy that you were rooting for.”

But when an officer moved to arrest him, Mr Brooks struggled with him and another officer at the scene before breaking free and running across the parking lot with what appears to be a police Taser in his hand, a bystander’s video showed.

A video from the restaurant’s cameras shows Mr Brooks turning as he runs and possibly aiming the Taser at the pursuing officers before one of them fires his gun and Brooks falls.

Atlanta’s police chief, Erika Shields, resigned over the shooting.

The officer suspected of killing Mr Brooks was fired, and the other officer involved in the incident, also white, was put on administrative leave.

As demonstrators in Atlanta took to the streets on Saturday and chanted for the officers in Mr Brooks’ case to be criminally charged, the Wendy’s restaurant went up in flames.

On Sunday, police offered a $US10,000 ($14,000) reward and published photos of what appeared to be a masked white woman being sought in connection with the case.

Police said they were seeking those responsible for the blaze, including a woman who was “attempting to hide her identity.”

Demonstrators set on fire a restaurant during the protest on June 13.

The department posted photos on social media of what looked to be a young white woman wearing a black baseball cap and face mask, and a video clip filmed by a protester that appeared to show a woman encouraging the flames.

“Look at the white girl trying to burn down the Wendy’s,” the man recording the video can heard saying. “This wasn’t us.”

Ms Bottoms said on Saturday that she did not believe the shooting was a justified use of deadly force.

Lawyers for Mr Brooks’ family said he was the father of a young daughter who was celebrating her birthday on Saturday. They said the officers had no right to use deadly force even if he had fired the Taser, a non-lethal weapon, in their direction.

Prosecutors will decide by midweek whether to bring charges, Fulton County District Attorney Paul Howard said on Sunday.

“(The victim) did not seem to present any kind of threat to anyone, and so the fact that it would escalate to his death just seems unreasonable,” Howard told CNN.

-AAP