VALLEJO, Calif. (KRON/AP) — A California police chief said an officer shot and killed a 22-year-old man during a night of violence because he thought the man had a gun in his waistband.

Vallejo Police Chief Shawny Williams said Sean Monterrosa, of San Francisco, was killed outside a Walgreens store shortly after 12:30 a.m. Tuesday as several people suspected of looting tried to flee police.

“I would say that it’s always a tragedy any time an officer has to use force. My condolences to his family. It is a difficult thing that happened,” Williams said.

Sean Monterossa (via GoFundMe)

Two cars fled the scene when officers arrived, but Monterrosa was not in them. He turned toward officers kneeling on the pavement as if he was preparing to shoot, Williams said.

“This individual appeared to be running toward the black sedan but suddenly stopped taking a kneeling position and placing his hands above his waist revealing what appeared to be the butt of a hand gun,” Williams said.

At that point, an officer sitting in an unmarked police cruiser fired his weapon through the windshield, the chief said. Williams did not identify the officer but said he is an 18-year veteran.

An investigation later revealed Monterrosa did not have a handgun but, instead, a 15-inch hammer tucked into the pocket of his sweatshirt.

“The district attorneys office will investigate this and decide whether or not this is a legal shooting or not,” Williams said.

A GoFundMe page for Monterossa describes him as “a wonderful son, brother, friend who touched the lives of those around him.”

The Associated Press contributed to this story.