The Aurora police officer who fatally shot an unarmed 17-year-old at a gas station in September was deemed to have used justifiable deadly force by District Attorney Amy Padden in a letter Friday.

In the letter to Aurora Police Chief Todd Chamberlain, Padden stated that she found Officer Derek Paulson “justified in using deadly physical force to defend himself and others” when he shot Blaze Balle-Mason.

The shooting happened Sept. 18 at a Conoco gas station, 290 S. Havana Street in Aurora, when officers responded to a call from Balle-Mason saying he was armed and going to “shoot the place up,” the decision letter said.

Balle-Mason told the 911 dispatcher that he was armed with a 9-mm pistol in the front pocket of his hoodie and that he would shoot at the police when they arrived because he was “tired of the cops,” the letter said.

Paulson and other officers responded to the gas station, where Balle-Mason approached them with his right hand in his hoodie pocket. Officers told him to show his hands and used a less lethal device to try to get him to comply, according to the letter.

The coroner noted several bruise marks consistent with the 40 mm less-lethal rifle used on Balle-Mason.

The suspect then ran toward the officers with his hand still in his pocket, and Paulson fired at him twice, hitting him once. He died at the scene, the letter said.

Investigators never found a gun on him.

“I find that Officer Paulson reasonably believed that Blaze Balle-Mason posed an imminent threat of deadly physical force to himself and the other officers in the area and was justified in using deadly physical force to defend himself and others from an apparent unlawful, imminent and threat of deadly physical force against him and the others,” Padden’s letter said. “Our office will not file criminal charges against him.”

The investigation was conducted by the 18th Judicial District Critical Incident Response Team and led by an Arapahoe County Sheriff’s Office investigator.