Police said they've arrested a man suspected of walking into a suburban Denver Walmart and immediately opening fire with a handgun, killing two men and a woman Wednesday night.

Thornton police said 47-year-old Scott Ostrem was arrested Thursday morning, about 14 hours after he fled the store in a car. Authorities used security video to help identify him.

Thornton police spokesman Victor Avila said Wednesday night that the shooting appears random and there are no indications that it was an act of terror.

He says the motive is unknown.

Police spokesman Victor Avila said a man nonchalantly entered the store and fired a handgun into a group of people before fleeing in a car. No one has been arrested.

"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."

The spokesman said there is currently no indication that the shooting was an act of terror.

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 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."

Investigators, who have not released any other details about the circumstances of the shooting, were reviewing security footage and interviewing witnesses.

Meanwhile, special agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives were helping police in the investigation.

The Walmart about 10 miles (16 kilometers) north of Denver is in a busy shopping center that includes restaurants, a movie theater and several other stores.

Ragan Dickens, a Walmart spokesman, said the company is working with investigators. He declined further comment.