Police say a shooting inside a suburban Denver Walmart is not an "active shooter" situation.
Local police earlier said that multiple people were shot inside a Walmart store in a Denver suburb.
Police spotted the vehicle and followed it, eventually stopping Ostrem in his Mitsubishi Mirage and taking him into custody. Two men were pronounced dead at the scene; a female victim was taken to an area hospital where she later died.
"We don't know exactly what the motive of the person was, but it was certainly a bad act", Avila said.
Police in Thornton announced the shooting in a tweet Wednesday evening and advised people to stay away from the area.
Two men died inside the Walmart, which is about 10 miles (16 kilometers) north of Denver in a busy shopping center.
"We've got multiple parties down, we're still trying to ascertain what their conditions are", Officer Victor Avila of the Thornton Police Department told Reuters.
"The employees started screaming and the customers started screaming".
Colorado authorities are searching for a man who police say nonchalantly walked into a Walmart and immediately opened fire, killing two men and a woman Wednesday night.