Officer Brentley Vinson reasonably believed he and fellow officers faced an imminent threat from Keith Scott, 43, who was armed with a cocked and loaded gun when they confronted him in the parking lot of a Charlotte apartment complex, District Attorney Andrew Murray told a news conference.
"Officers can be heard at least 10 times ordering Mr. Scott to drop the gun," Murray said. "Mr. Scott did not comply with those commands."
Scott's family has denied he had a weapon during the Sept. 20 incident, which sparked a week of sometimes violent protests in Charlotte, North Carolina's largest city and a U.S. banking hub.
But Murray said "all of the credible and available evidence suggests that he was, in fact, armed."
The shooting made Charlotte another flashpoint in two years of protests over police killings of black men, many of them unarmed, across the country.
A day after Scott was killed, demonstrators took to the streets in the upscale urban area known as "Uptown," where some looted businesses, smashed windows and blocked traffic.
Dozens of people were arrested, and a man was fatally shot amid the chaos.