CHARLOTTE, N.C. (Reuters) - A police officer “acted lawfully” when he shot and killed an armed black man in Charlotte, North Carolina, in September and will not face criminal charges for his use of force, a district attorney said on Wednesday.

Officer Brentley Vinson reasonably believed he and several other officers faced an imminent threat from Keith Scott, 43, who they saw holding a 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,” the prosecutor said, referring to videos of the incident. “Mr. Scott did not comply with those commands.”

The decision not to prosecute Vinson raised fears of fresh protests in Charlotte, North Carolina’s largest city and a U.S. banking hub. Scott’s death on Sept. 20 sparked a week of sometimes violent demonstrations, making the city another flashpoint in two years of protests over police killings of black men, many of them unarmed, across the country.

Nearly 100 people gathered in the rain Wednesday night outside the city’s police headquarters, where chants included, “the whole damn system is guilty as hell.” Protesters, who were spirited but not violent, then began marching in the area where earlier this fall people smashed windows and looted businesses.

Four people were arrested for obstructing traffic during the “mostly peaceful” protest, Charlotte-Mecklenburg Police Department said on Twitter. One was also charged with disorderly conduct, police said.

Scott’s family said in a statement they were “profoundly disappointed” by prosecutors’ findings, but they asked “that everyone work together to fix the system that allowed this tragedy to happen in the first place.”

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The family and people who said they witnessed the shooting disputed that he had a weapon. Some said the father of seven was instead holding a book and was shot by a white officer, rather than Vinson, who is black.

The district attorney said the two-month investigation disproved those claims.

Murray showed surveillance footage from a convenience store Scott visited minutes before the shooting that showed a bulge in his pants near his right ankle. That was consistent with the holster and gun later described by officers and located at the scene, the prosecutor said.

Murray acknowledged that none of the video recordings from the scene offered clear evidence that Scott was holding a gun when he was shot.

However, Murray said, “all of the credible and available evidence suggests that he was, in fact, armed.” Several self-described eyewitnesses did not actually see the incident, he added.

Analysis of all the officers’ guns confirmed Vinson was the only one who fired his weapon.

The officers described Scott as having a blank stare “as if he was in a trance-like state,” consistent with the side effects of a medication Scott’s wife confirmed he had been taking, Murray said.

The prosecutor said Scott’s DNA was found on his gun, which was cocked with the safety off and a round in the chamber.