UPDATE: 10/10/18

The man who opened fire in a Colorado Walmart, killing 3 people, will likely spend his life in prison. Today he pleaded guilty in the case to avoid the death penalty.

Over the summer, Scott Ostrem was found mentally competent to stand trial.

Today, almost a year after the crime, he pleaded guilty to three counts of first-degree murder and one count of attempted first-degree murder.

Ostrum will be sentenced to life in prison without parole next Friday in Adams County.

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The alleged gunman in a shooting rampage at a suburban Walmart was taken into custody Thursday after leading police on a car chase.

On Friday, he made his first court appearance. On Monday, prosecutors filed murder and attempted murder charges against him. Authorities made no mention of a possible motive for the attack during a hearing for 47-year-old Scott Ostrem.

The murder charges carry a sentence of life without parole or the death penalty. Prosecutors have not said whether they'll seek Ostrem's execution.

The judge scheduled a Feb. 5 preliminary hearing for prosecutors to lay out their case. The judge will decide if the evidence is sufficient for a trial.

Walmart Shooting Suspect Court Appearance Thornton Walmart shooting suspect Scott Ostrem is making his first appearance in Adams County Court. Watch it live. http://cbsloc.al/2zbXC2I Posted by CBS Denver on Friday, November 3, 2017

Ostrem is accused of walking into a Walmart in Thornton Wednesday evening and opening fire on a group of people. Then as abruptly as the rampage started, he strolled back out, went to his car and drove off.

Two men were left dead in the store and a third victim, a woman, died a short time later at the hospital. On Thursday, Coroner Monica Broncucia-Jordan identified the victims as 52-year-old Pamela Marques, 66-year-old Carlos Moreno, and 26-year-old Victor Vasquez.

Based on the preliminary investigation, Thornton police believe the attack was random.

"What we've determined is that it is random as of right now because there was no direction or anything like that. As the witnesses stated, the person just came in and shot towards the group," said Thornton Police Department spokesperson Officer Victor Avila.

Avila said the suspect walked through the store's main entrance on the southern side of the building's storefront and opened fire near the cash registers. Despite firing into a group, only the three victims were hit.

"There were other people who did receive medical attention, but for anxiety and things like that," he said.

The shooting started just after 6 Wednesday night at the Walmart on 9901 Grant St. The store is located by a shopping center and movie theater.

"Terror," Jessica Israel told 11 News the first feeling she had when she heard her nephew was at the Walmart. "I'm just wondering what's going on and if he's okay, I've heard stories worrying about who else is in there and what's going on."

Israel told 11 News she heard stories about people inside the store pulling down laundry bins to hide and other trying to find cover under anything.

"It's insane," added Jessica. "It started off with a large police presence and as the night went on it just got bigger."

At the time 11 News spoke with her, Israel had been searching for her nephew for more than two hours. Sister station KCNC is reporting that four dozen people were transported via buses to the Thornton Police Department headquarters to be reunited with their families, but we have not confirmed if Israel's nephew was among them.

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

Guadalupe Perez told KCNC she thought it was balloons popping at first. She was shopping at the store with her little boy at the time.

"We were renting movies and we just heard this popping noise. The Walmart girl said, 'The balloons are popping.' As I turn around and I just see all the people walking, falling down because they were really scared. I just told them, 'What's going on?' and they were like, 'They're shooting!' They're shooting!'"

Special agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives were called to the scene to help police.

Ostrem was identified as a person of interest Wednesday night and upgraded to a suspect Thursday morning. Thornton police said they quickly determined where he lived, but he wasn't home when they executed the search warrant. But he did not leave the metro area after the shooting or ditch his vehicle, and officers caught up with him Thursday driving in the red Mitsubishi he had allegedly been seen leaving Walmart in the night before. He was just 7 miles from the crime scene.

The Thornton Police Department held a news conference after Ostrem was captured.

Thornton Police News Conference Watch the news conference by Thornton PD. The suspect in the Walmart shooting is in custody. http://cbsloc.al/2zs8gmJ Posted by CBS Denver on Thursday, November 2, 2017

Ostrem has reportedly been arrested in Colorado 14 times, but primarily for minor infractions. His criminal history before Wednesday night was minimal, according to Avila.