Two men and a woman were killed in gunfire inside a Denver suburb and Walmart, forcing the agents to hide or flee.
Thornton Police reported “several limbs fallen” and advised people to stay away from the area as dozens of police cruisers and emergency vehicles rushed to the scene.
The men died in the store, and the woman died in the hospital.
Police spokesman Victor Avila said a man carelessly entered the store and fired a pistol at a group of people before fleeing in a car. No one has been arrested.
“This is a very heinous act,” said Avila. “We don’t know exactly what motivated that person, but it was definitely a horrific act.”
The spokesman said there was currently no indication that the shooting was a terrorist act.
Aaron Stevens, 44, was in self-exiting queue when he heard one shot followed by two more bursts of fire before people started running to the exits.
“The staff started screaming. The agents were screaming. They were running like crazy, and I ran away too because I didn’t want to be killed,” he said.
Guadalupe Perez was inside the store with her young son when she heard what she thought was a balloon exploding. A Walmart employee told her someone was shooting, and then Perez saw people running away shouting, “Let’s go. Let’s go. Leave the grocery.”
“You see all this stuff on the news and you go through it,” she said. “It’s scary.” But thank God we are fine and nothing happened to us.
The investigators, who did not release any other details about the circumstances of the shooting, reviewed the security footage and interviewed witnesses.
Meanwhile, special agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives were assisting the police in the investigation.
Walmart is located about 10 miles (16 kilometers) north of Denver in a busy shopping center that includes restaurants, a movie theater, and many other stores.
Rajan Dickens, a spokesman for Walmart, said the company was working with the investigators. He declined to comment.