Four people are dead and at least three injured, including a police officer, after what authorities are calling a “killing spree” in the Denver and Lakewood, Colo. area on Monday, The Washington Post reports.

Denver police have since launched a “large-scale” investigation into the incident, and are working to establish a motive, NBC News reports. The still-unidentified suspect eventually died in a shootout with police in the suburb of Lakewood, though Lakewood police spokesman John Romero said he was “still unsure” if community police had shot him, per the Post.

Law enforcement has also emphasized their belief that “the shootings were the work of one person and the community faced no further threats,” writes the Post. 

The “rampage” is believed to have begun around 5 p.m. local time in Denver, where “two women died, and one man was injured,” writes the Post. Another man was reportedly killed nearby before police identified the suspect’s car and exchanged gunfire, unable to stop the shooter from fleeing to neighboring Lakewood, where another victim was later pronounced dead. When confronted by police in Lakewood’s Belmar neighborhood, the gunman fled on foot into a Hyatt hotel, where he is reported to have shot a clerk, who is now hospitalized. After fleeing again, a shootout between authorities and the suspect ensued, with the shooter eventually “taken down,” Romero said.

“This is the holiday season,” added Denver police chief Paul Pazen, per The New York Times. “To have this type of spree take place is not normal for our community.”