Cop Who Shot Keith Lamont Scott 'Acted Lawfully,' DA Says Scott was shot and killed by an officer in September.

 -- Prosecutors decided today not to file criminal charges against Brentley Vinson, the Charlotte-Mecklenburg police officer who shot Keith Lamont Scott in September.

Mecklenburg County District Attorney Andrew Murray said in a press conference that Vinson "acted lawfully," and declared that the incident was a “justified shooting based on the totality of the evidence” because the officer perceived an imminent threat.

Murray said 15 veteran prosecutors in his office were unanimous in their recommendation not to charge Vinson with a crime.

In the wake of the decision, protests broke out in Charlotte. Four protesters were arrested, police said Wednesday night.

Scott's death sparked days of protest and unrest in Charlotte, North Carolina, after a series of videos of the encounter were released to the public.

Murray said that he had spoken to Scott's family, and described them as being "extremely gracious."

Scott was shot once in the back, an autopsy report showed, as well as his wrist and abdomen, the latter of which ultimately caused his death.

Scott's death played into widespread concerns in the U.S. about the way black men are treated by police, and occurred days after Terence Crutcher, a Tulsa, Oklahoma man, was also killed by police in a videotaped encounter that was widely shared on social media.

Police have maintained that Scott was holding a handgun. Police Chief Kerr Putney previously said that he would release "indisputable evidence" supporting that claim. However, Murray said today that “none of the footage we’ve seen shows Scott’s hands.” Murray added that Scott’s gun was found at the scene, loaded and cocked with the safety off.

Today, Murray showed surveillance video of Scott taken at a local 7-Eleven before he was shot. The video appears to show a bulge around Scott's ankle as he entered the convenience store. Murray said that bulge may have carried a gun.

Murray then showed a still image taken after Scott had parked his SUV in the apartment complex lot where he was shot. That image appeared to show no bulge in the same spot around Scott's ankle. Murray said that officers witnessed a gun in Scott's hands prior to the encounter taking place.

Scott’s family initially claimed that he was holding a book, and not a gun, at the time he was shot, and that Scott was unarmed.

“I can tell you we did not find a book that has been referenced to,” Putney told reporters in September.

According to Putney, officers said they saw a weapon and marijuana in Scott's car while they were doing surveillance for an unrelated warrant for someone other than Scott. Murray said today that Scott was taking drugs at the time he was shot, which he described as “mind-altering.” In addition to smoking marijuana, Scott was taking medication to treat a traumatic brain injury he sustained from a motorcycle accident, according to the Scott family attorney.

The chief said Scott ignored repeated commands to drop the weapon, prior to the shooting taking place.

Today, the Scotts' attorney said that based on current evidence, Scott had a firearm, but there was no definitive proof that the gun was in his hand. He added that the family would take the case to civil court, if family members decided that it was appropriate.

Legal experts have told ABC News that if Scott did carry a gun at the time he was killed, its presence would not be enough to forcibly disarm him according to state law.

North Carolina is a so-called open carry state.