Arvada, Colorado, rampage came 2 days after Gov. Polis signed gun bills in response to Boulder shootings

Authorities in Colorado tried to determine Tuesday what prompted a shooting spree in a suburban Denver shopping district that left a police officer, bystander and suspect dead.

The shooting Monday afternoon in Old Town Arvada came two days after Colorado Gov. Jared Polis signed three gun control bills in response to another shooting – a gunman's rampage at a Boulder supermarket 20 miles away that killed 10 people three months ago.

The bills require expanded background checks before gun purchases and reverse a ban that kept local governments from creating their own gun regulations. The state is creating an Office of Gun Violence Prevention.

"My thoughts are with the family and friends of those killed including an Arvada Police Officer who was tragically killed in the line of duty while swiftly and bravely responding to protect civilians," Polis tweeted late Monday.

Arvada police provided few details on the carnage. Police responded to a suspicious incident near a library in the area, then received a 911 call about 15 minutes later reporting shots fired, Deputy Police Chief Ed Brady said.

The bystander was identified only as a "Samaritan." The officer was 19-year police veteran Gordon Beesley, who was a school resource officer known for developing relationships with students, city officials said.

While school was out for the summer, Beesley was working on patrol when he was hit by gunfire.

According to his school resource officer biography, he played the drums in a band and enjoyed hiking, biking, skiing and camping with his family. His motto was “Look for the good in every day.”

Brady Turner, 18, was eating lunch at the Arvada Army Navy Surplus store when he heard three gunshots and screaming. He told the Denver Post he fled the area.

“I was looking in all directions to make sure no one was following me,” he said.

Gunfire erupts: 3 killed in Denver-area shooting, including a police officer and suspect, authorities say

Employees at the Arvada Chamber of Commerce, less than a block from the shooting site, sheltered in the building’s basement for more than an hour after the gunfire subsided.

“Our hearts are with the Arvada Police Department and all who were impacted today,” Chamber President Kami Welch said in a statement to the Post.

Mayor Marc Williams said he was driving in the area when he saw about a dozen police cars with their flashing lights and sirens race past.

"I knew something serious had happened," he said. "I didn’t know how serious.”

A phalanx of police officers in a lengthy procession of vehicles accompanied the slain officer’s body from the scene to the Jefferson County Coroner’s Office. Scores of residents gathered to pay respect to the officer.

"Remember Officer Beesley and all the lives he touched during his career," tweeted Colorado State Patrol Troop 2C. "Blessed are the peacemakers. #ThinBlueLine"

Contributing: Elinor Aspegren, USA TODAY; The Associated Press

This article originally appeared on USA TODAY: Colorado shooting came 2 days after Gov. Polis signed gun bills