The North Carolina cop whose shooting of a black man in September touched off riots and helped fan fanned racial flames around the nation will not face charges, a prosecutor said Wednesday as he painstakingly laid out evidence the dead man brandished an illegal gun at police and ignored repeated commands to drop it.

Charlotte-Mecklenburg District Attorney Andrew Murray determined that Officer Brentley Vinson's actions in killing Keith Lamont Scott were justified.

“We cannot know what Scott’s intention was that day,” Murray said.

Scott's family has said he was not armed.

Murray held an extensive news conference and displayed a nearby store's surveillance video showing the outline of what appeared to be a holstered gun on Scott's ankle, and he gave extensive details about other evidence that Scott was armed.

Prior to any confrontation, Vinson informed another officer that he saw Scott with a gun, Murray said. Officers at the scene said after Scott was shot, the gun fell to the floor.

"Mr. Scott's DNA was found on the slide of the gun and the grip of the gun," Murray said. The Charlotte police crime lab found Scott's fingerprints on the gun, but the state crime lab "did not find that print to be of value."

Murray said a Colt .380 semi-automatic was recovered at the scene with one live round in the chamber with the safety off. The gun was cocked.

"Mr. Scott illegally purchased the gun on Sept. 2," Murray said. The seller admitted to selling the gun to a third party on Facebook.

"Basically the seller saw, what we all saw, the video of the incident and said, 'I know that guy and I know that gun," Murray said.

Plainclothes officers had gone to the complex about 4 p.m. on Sept. 20 looking for a suspect with an outstanding warrant when they saw Scott -- not the suspect they were looking for -- inside a car with a gun and marijuana, department spokesman Keith Trietley has said in a statement.

Officers saw Scott get out of the car with a gun and then get back in, police said. When officers approached, they said, Scott exited the car with the gun again. At that point, officers deemed Scott a threat and Vinson fired his weapon.

Scott, 43, was pronounced dead at Carolinas Medical Center. An autopsy report from Mecklenburg County authorities says Scott died of gunshot wounds to the back and abdomen.

Vinson, who is also black, had been with the department for two years at the time of the shooting. He has been on administrative leave which is standard in police shootings.

At a Wednesday news conference, Murray said an expert determined that all four shell cases that were fired were from Vinson's gun.

Body camera and dashcam recordings released earlier by the police department did not conclusively show that and city officials were criticized for the length of time it took to release police video of the shooting.

Scott's final moments also were recorded by his wife, Rakeyia, in a video shared widely on social media. She can be heard shouting to police that her husband "doesn't have a gun." She pleads with the officers not to shoot before a burst of gunfire can be heard.

The shooting led to two nights of violent protests, including a fatal shooting in downtown Charlotte the next night. The unrest gave way to several more days of largely peaceful demonstrations, and the city instituted a curfew for multiple nights.

FoxNews.com's Edmund DeMarche and The Associated Press contributed to this report