At about 6:10 p.m. on Wednesday, someone with a gun shot and killed three customers inside of a Walmart in Thornton. That person then left the store.

Three hours after the shooting, 9NEWS reporter Steve Staeger confirmed with police that there was no suspect in custody. Police themselves didn’t officially speak to the media for the first time until 11:15 – five hours after the shooting – when they formally announced to the public they were searching for a shooter.

An empty lecturn stands near the Walmart where three people were shot and killed. Police eventually gave their first press conference at 11:15 p.m.

Thornton Police gave burst updates on Twitter throughout the night, but the public wasn’t aware of the shooter’s status based on those tweets.

At a press conference Thursday morning, Victor Avila, a public information officer with Thornton Police, described the scene as mass chaos. Another public information officer, Matt Barnes, told 9NEWS that they didn’t even know the shooter fled initially, nor how many shooters there were.

Officers had to clear the scene enough to allow a Walmart employee inside of the store, so they could determine who the suspect was based on pictures. Avila said:

“We had hundreds of people self-evacuating from a large establishment so we've got people leaving, we've got cars leaving so we've got officers out there trying to be able to cordon off the area to determine that's an actual suspect that's leaving. We did that as quickly as we could. Again, we had to render the area safe. We can't just send somebody in -- an employee from Walmart -- to start reviewing the footage. So once we were able to safely allow a Walmart employee in to start going over the footage, we had detectives come in and we started to go over the footage.”

Walmart's corporate office told Next with Kyle Clark that a store's surveillance video can be accessed remotely through Walmart's own proprietary system, but only at the headquarters in Bentonville, Ark. Staff at the headquarters can share the images and video with police when requested, so investigators don't need to wait to enter a store. But, if police want to see the footage for themselves and confirm they have the correct suspect, they have to enter a store and see the video there.

According to Barnes, officers flooded surrounding neighborhoods while other officers simultaneously vetted possible suspects, reviewed surveillance footage and searched the building and surrounding property. The Thornton Police Department told 9NEWS that because officers were saturating those nearby neighborhoods, police did not feel there was an immediate threat to the area.

In the Thursday press conference, Avila added that other people in the store with guns, who had been carrying them with concealed carry permits, slowed the process of finding a suspect.

“That was part of what we encountered on surveillance. We had to be able to discern what exactly was going on; whether that was a suspect, or whether that was a citizen truly worried about what was going on and hearing the sound of the gunshots,” he said.

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Thornton Police told 9NEWS that multiple people were detained Wednesday night in the process of searching for a suspect.

Next spoke with former a former FBI special agent in charge of the Denver area, Bob Pence, who was recently at a law enforcement conference where the topic of police response in situations like this arose.

“I think you have to have confidence in the police department that they are going to make the decision based on the best practice for whatever the situation is in that case,” Pence said.

But, he said, it’s becoming more common practice for police to get information out to the media quickly to prevent speculation on social media.

“You say here’s what we know and we don’t know everything and we’re probably going to know new stuff or stuff is going to change,” he said.

According to Pence, social media has changed the way police respond to active shooter situations like this. He says it can be both a dangerous and helpful tool.

“Law enforcement agencies have to monitor the social media so they know that something was just tweeted that’s absolutely not correct and it might cause a lot of problems because it might cause panic it might cause all kinds of ramifications they don’t want,” he said.

Social media can also give police extra leads in a case, which is why public information officers monitoring the web can be helpful in situations like this.

Still he says departments shouldn’t solely rely on sending updates through Twitter and Facebook. People need to see a real person.

“It shows they care enough to actually put a face out to say here’s what we know,” he said. “If the police don’t say something about something when they can and when they should...somebody else is because this is the day of instant communication.”