Thornton police say 47-year-old Scott Ostrem was arrested Thursday morning, about 14 hours after he fled the store in a auto. A little more than an hour later, they tweeted that there was no longer an active shooter at the scene "at this time".
They also confirmed that no suspect was yet in custody.
Two men died inside the Walmart, which is about 10 miles (16 kilometers) north of Denver in a busy shopping center.
Avila said there was no indication the shooting was an act of terrorism as no one has claimed responsibility. "We don't know exactly what the motive of the person was, but it was certainly a bad act". The Walmart girl said, 'The balloons are popping.' And I turn around and I just see all the people walking, falling down because they were really scared. "Then I heard two more shots and I freaked out and hit the ground". "A lady came running back, screaming about the shots", Thompson told the Denver Post.
"I immediately froze because I didn't know what to think or what was going on", Aaron Stephens explained to CBS 4.
Almost 50 witnesses were reportedly taken to a nearby police station in the wake of the shooting before being released.