DENVER, Colorado - Police arrest man suspected of opening fire, killing 3 people at Colorado Walmart. 

The shooting happened inside the store on Wednesday night.   

Thornton police reported "multiple parties down" and advised people to stay away from the area as dozens of police cruisers and emergency vehicles raced to the scene.

The men died at the store, and the woman died at a hospital. 

Thornton Police tweeted a picture of a person of interest.

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.

"I immediately froze because I didn't know what to think or what was going on. Then I heard two more shots and I hit the ground,"  witness Aaron Stephens told CBS Denver.  

"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.
Investigators were reviewing security footage and interviewing witnesses to get a description of the shooter.  Special agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives were helping police in the investigation.

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