The violence unfolded at the Kings Sooper store in Boulder on Monday afternoon and the shooter’s motive has not been determined, law-enforcement officials told the Wall Street Journal.
A partially clothed white male was seen being led away from the scene in handcuffs with blood covering his leg.
“My heart is breaking as we watch this unspeakable event unfold in our Boulder community,” said the state’s governor Jared Polis in a statement on Twitter.
At a press conference on Monday evening, Commander Kerry Yamaguchi of the Boulder Police Department confirmed that 10 people had died.
“We had a very tragic incident today. There was loss of life, we have multiple people who were killed in this incident, and I am sorry to have to report that one of them was a Boulder police officer.”
“There is no ongoing public threat we have a person of interest in custody, that person was injured during the incident and is being treated for the injuries.”
“The only injured party we are aware of was the suspect. We know of no other serious injuries at this point,” added Commander Yamaguchi.
Eyewitnesses inside the store told of the horror as the shooting began.
Two customers told the Denver Post that they were buying lunch when the shooting broke out.
“He didn’t say sh**,” one said. “He just came in and started shooting.”
The other said the gunman “let off a couple of shots, then was silent, and then he let off a couple more”.
The pair were among the shoppers who fled in a “stampede” to the back of the store.
Images and haunting video from the scene revealed a half-clothed man covered in blood being escorted to a stretcher by police.
Bodies of victims outside the store were also captured.