A man has been arrested on suspicion of walking into a suburban Walmart in Colorado in the US and opening fire with a handgun, killing two men and a woman.
Thornton police said 47-year-old Scott Ostrem was arrested this morning, about 14 hours after he fled the Denver store in a car.
Authorities used security video to help identify him.
Police spokesman Victor Avila said on Wednesday night that the shooting appeared random and there are no indications it was an act of terror.
Two men died inside the Walmart, which is about 10 miles (16km) north of Denver in a busy shopping centre. The woman died later at a hospital.
The shooting forced customers to hide or flee and police reported "multiple parties down".
They advised people to stay away from the area as dozens of police cars and emergency vehicles raced to the scene.
Mr Avila said a man nonchalantly entered the store and fired a handgun into a group of people before fleeing in a car.
"This is a very heinous act," he said. "We don't know exactly what the motive of the person was, but it was certainly a terrible act."
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.
"The employees started screaming. Customers were screaming. They were running like crazy, and I ran out too because I didn't want to get killed," he said.
Guadalupe Perez was inside the store with her young son when she heard what she thought was a balloon popping.
A Walmart employee told her someone was shooting, and then Ms Perez saw people running away yelling: "Let's go. Let's go. Leave the groceries."
"You see all these things in the news and you go through it, it's scary," she said. "But thank God we're OK and nothing happened to us."
Special agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives were helping police in the investigation.
Ragan Dickens, a Walmart spokesman, said the company was working with investigators.
Neighbours described Ostrem as a hostile loner who often carried a shotgun in and out of his third-floor apartment.
Residents of the Samuel Park Apartments building where Ostrem lived described him as a rude man who kept to himself.
Most of the building's tenants talk to each other, but Teresa Muniz said Ostrem never returned her greetings and swore at people for sitting on exterior stairways and leaving laundry in communal machines.
"He didn't seem to have anybody," she said. "Being angry all the time. That's what he seemed like, always angry."
She said she sometimes saw Ostrem carrying a shotgun or a bow and set of arrows to and from the building.
Gerald Burnett, a 63-year-old retiree who lives in a first-floor apartment, said: "He's the type of person if you said 'good morning,' he wouldn't say nothing. If you greeted him, he wouldn't say anything back. I just learned not to even talk to the clown."