The suspect, whom authorities have yet to publicly identify, reportedly opened fire at a Colorado Springs birthday party, killing six adults.
A birthday party at a mobile home community in the USA city of Colorado Springs descended into violence when a man whose girlfriend was attending opened fire at the revelers, police said Saturday.
Police confirmed that none of the children were injured in the attack.
Among the incidents this year was one in Boulder, Colorado, where a 21-year-old man has been charged with killing 10 people in a March 22 shooting spree at a supermarket about 30 miles (50 km) northwest of Denver.
Anyone who has information about the shooting can call the Colorado Springs Police Department at (719) 444-7000 or Crime Stoppers Tip Line at (719) 634-STOP (7867) or 1-800-222-8477.
The birthday party was for one of the people who was killed, the outlet noted.
It took place as Americans observed Mother's Day on Sunday, "celebrating the women in our lives", Colorado Governor Jared Polis said in a statement.
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Neighbor Yenifer Reyes said that she heard the gunshots and thought they were thunder. "Then I started hearing sirens", Reyes told the newspaper.
All of the victims, whose names and ages have yet to be released, were adults.
There were children inside the home who were hysterically crying, but they were not targeted, the report said.
"Today we find ourselves mourning the loss of lives and praying solemnly for those who were injured and those who lost family members in a senseless act of violence on Sunday morning", said Colorado Springs Mayor John Suthers in a statement.
"Multiple lives were taken today by this bad act of violence". Like Polis, he said he was grieving with those lost at the birthday party.
After that incident, as well as a mass shooting incident in Atlanta, President Joe Biden and Democrats in Congress issued a series of gun-control proposals, while the House of Representatives passed two gun background check laws. From the officers who responded to the shooting to the investigators still on scene, we are all left incredibly shaken.