A policeman repeatedly kicked Rayshard Brooks as he lay fighting for life after being shot by the officer, Atlanta prosecutors say.
Videos from the scene of the alleged murder also reveal another policeman stood on Mr Brooks and neither officer provided the dying man first aid for more than two minutes.
Fulton County District Attorney Paul Howard confirmed on Thursday morning (Australian time) that Officer Garrett Rolfe, who twice fired his gun at the 27-year-old victim, had been charged with murder and 10 other offences.
Officer Rolfe could face the death penalty or life in prison if convicted.
“Mr Brooks was running away … he was shot twice in the back,” Mr Howard said.
“He did not pose an immediate threat of death or serious physical injury to the officers.”
Mr Brooks, a married father who lived locally, had fallen asleep in the driveway of a Wendy’s takeaway restaurant.
When police arrived, they woke him and asked that he move his car.
Video and audio showed that after moving the car, Mr Brooks offered to leave it there and walk home.
Mr Howard said the victim had been “cordial” and “almost jovial”, politely answering police questions in the carpark for 41 minutes and 17 seconds, even though he was not under arrest.
“He received many instructions from the Atlanta officers … he followed very instruction, he answered the questions,” he said.
“Mr Brooks was never informed that he was under arrest for driving under the influence.
“He was grabbed from the rear by Officer Rolfe, who made an attempt to physically restrain him.”
Video released after Mr Brooks’ death showed that he had struggled with the officers and had run away with a police stun gun.
Mr Howard said the taser had already been discharged twice when Officer Rolfe fired at Mr Brooks as he ran away.
The policeman should have known that the taser was no longer a threat and that Mr Brooks was running away and therefore of no threat, the state will argue.
The death of Mr Brooks, a black man, happened last Friday amid protests across the US – and other countries, including Australia – against police brutality and racial injustice.
The shooting sparked a new wave of demonstrations in Georgia’s capital after the sometimes violent protests that erupted in response to the death of unarmed black man George Floyd who was pinned under a police officer’s knee in Minneapolis.
Mr Howard said state prosecutors had studied videos and spoken to 10 witnesses, some of whom were in danger from stray bullets during the police shooting in the Wendy’s carpark.
In a decision Mr Howard said was a state first, Officer Devin Brosnan has indicated he is willing to testify against his colleague.
“What he has said to us … he plans to make a statement regarding the culpability of Officer Rolfe,” Mr Howard said.
Officer Brosnan has also been charged for standing on Mr Brooks.
“Officer Brosnan has admitted that he was, in fact, standing [on Mr Brooks],” Mr Howard said.
The pair has a day to surrender to police.