The shooting at Old National Bank in Louisville, Kentucky, began around 8:30 a.m. ET, police said, about 30 minutes before the bank opens to the public.

Bank staff were holding their morning meeting in a conference room when the shooter opened fire, Rebecca Buchheit-Sims, the bank manager, said.

One bank employee frantically called her husband as she sheltered inside a locked vault, the husband, Caleb Goodlett told CNN affiiliate WLKY. By the time he called 911, police were already aware of the shooting, he said.

“Just a very traumatic phone call to get,” Goodlett told the affiliate, adding that he has since seen his wife and she is OK.

The gunman, who was still firing when police arrived, was killed in a shootout with officers, police officials said.

Nickolas Wilt, a 26-year-old rookie officer, ran toward the gunfire and was shot in the head, interim Louisville Metro Police Chief Jacquelyn Gwinn-Villaroel said. He had graduated from the police academy just 10 days before the shooting. Wilt underwent brain surgery and was in critical but stable condition as of Monday afternoon, the chief said.

The gun used in the shooting was an AR-15-style rifle, a federal law enforcement source told CNN. The semi-automatic rifle is the most popular sporting rifle in the US, and 30% of gun owners reported having owned an AR-15 or similar-style rifle, according to the 2021 National Firearms Survey. The AR-15 and its offshoots have been the weapon of choice in many of the most horrific mass shootings in recent memory, including the Covenant school shooting in Nashville just two weeks ago.

The bank sits on the fringe of Louisville’s developing downtown business district, state Sen. Gerald Neal, who represents the district where the shooting happened, told CNN. 

CNN’s John Miller, Laura Ly, Artemis Moshtaghian, Celina Tebor, Caroll Alvarado, Kristina Sgueglia, Sara Smart and Eric Levenson contributed to this report.