A man nonchalantly walked into a Walmart and immediately opened fire with a handgun, killing two men and a woman before fleeing in a car on Wednesday night, according to Colorado authorities.
The shooting appears random and there are no indications that it was an act of terror, said Thornton police spokesman Victor Avila.
"This is a very heinous act," Avila said. "We don't know exactly what the motive of the person was, but it was certainly a terrible act."
Two men died inside the Walmart, which is about 16km north of Denver in a busy shopping centre. The woman died later at a hospital.
Authorities did not immediately release any other information about the victims.Aaron Stephens, 44, was in the self-checkout line when he heard a single shot followed by two more bursts of gunfire before people started running for the exits.