THORNTON, Colo. (NBC) - A SWAT team on Thursday morning arrested the suspect wanted in connection with the killing of three people at a suburban Denver Walmart, police said in a tweet.
His capture comes less than two hours after police in Thornton, Colorado, identified the suspect as Scott Ostrem, 47, and said they issued a homicide warrant for his arrest.
The circumstances surrounding his capture, which followed an overnight manhunt, were not immediately known.
Ostrem was nonchalant and appeared to be firing randomly with a handgun at people near the cash registers of the Walmart in Thornton, police said. They added that it was unknown if the attack was related to terror.
"This is a very heinous act," said Thornton police spokesman Victor Avila. "We don't know exactly what the motive of the person was, but it was certainly a terrible act."
The first calls were reported at 6:10 p.m. local time (8:10 p.m. ET) and the gunman — described as wearing a black jacket, blue jeans and a maroon shirt — fled in a red 2017 Mitsubishi Mirage with Colorado license plates.
Two men were killed at the scene, while a woman later died at the hospital, police said. The victims were not immediately named.
Hundreds of emergency vehicles rushed to the Walmart, located in a busy shopping center, where customers ran out of stores in panic and families waited anxiously to reunite with their loved ones in the parking lot.
Aaron Stephens, 44, was in the self-checkout line when he heard a single shot followed by two more bursts of gunfire before people bolted for the exits.
"At first I thought it was a firecracker," he told KUSA, "but it sounded more — it was louder... I was like, 'What the heck's going on?' Then I heard two more shots and I freaked out and hit the ground."
Guadalupe Perez was inside the store with her young son when she heard what she thought was a balloon popping.
A store employee told her someone was shooting, and then Perez saw people running away yelling, "Let's go. Let's go. Leave the groceries."
Investigators, including special agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives, were reviewing security video and interviewing witnesses. Avila said police don't yet know how many rounds were fired.
Forty-eight witnesses from the scene were interviewed by investigators.
Walmart said in a statement that it was "deeply saddened by this tragic event" and was assisting law enforcement. It also said all of its employees were accounted for and uninjured.
Stephens said he can't forget the frightened looks as fellow shoppers and Walmart employees ran for their lives.
"I didn't want to die," he said. "Here's Las Vegas happening in Colorado — at that moment all I could think about was my life."
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