Anna Thallas speaks to reporters about a bill requiring people to report lost and stolen guns. (Jesse Paul, The Colorado Sun)

A police sergeant in Denver has resigned nearly a year after his longtime friend used the officer’s personal gun in a fatal shooting.

The Denver Post reports that Sgt. Dan Politica did not state a reason for leaving when he resigned March 13.

The officer’s personal AK-47 rifle was used in a shooting that happened June 10, 2020, when Michael Close opened fire at Isabella Thallas, 21, and her boyfriend, Darian Simon, in broad daylight in downtown Denver after an argument about their dogs.

Thallas died, Simon was wounded, and Close has since pleaded not guilty by reason of insanity.

Police said Close had taken the gun without permission and just minutes after the shooting, the gunman called his friend of about 20 years to tell him he had “done something really bad” and “there’s no going back from this now.”

Politica notified the police department after he discovered his rifle was missing and that it may have been used in the shooting. The officer also told investigators that he had been worried about Close’s mental health.

Denver police spokesman Jay Casillas said there wasn’t an open investigation into Politica’s conduct at the time of his resignation.