Police scanner audio from Monday’s mass shooting at a King Soopers in Boulder, Colorado reveals the chilling moments that led up to the apprehension of the suspect.

"Be advised the suspect is armed with a rifle, unknown location inside," an officer can be heard saying on the audio obtained by Fox News, while coordinating with other officers at different locations around the building.

Police stand outside a King Soopers grocery store where authorities say multiple people have been killed in a shooting, Monday, March 22, 2021, in Boulder, Colo. (AP Photo/David Zalubowski)

Another officer can be heard saying they need to bring in a SWAT team with rifle shields because an officer is "down" about 30 yards inside the store and can’t be reached.

"We have no known location of the shooter. We think he might be setting up an ambush," he says, sounding calm and focused. 

Later, the officers are able to obtain a visual of the suspect inside the store via a video feed.

"We’ve got a couple of bodies down close to the entry of the store," a dispatcher can be heard saying.

A Denver SWAT team arrives and is deployed to the roof of the building. An officer can be heard advising his department and SWAT team to proceed cautiously because they still do not know the exact location of the suspect.

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The SWAT says it has "made contact" with a "possible suspect" and Boulder police order another team to scour the building to verify there are no other suspects.

Police on Tuesday identified the shooting suspect charged with killing 10 people as 21-year-old Ahmad Al Aliwi Alissa. Alissa, who is from the Denver suburb of Arvada, was booked into the county jail Tuesday on murder charges after being treated at a hospital.

Boulder shooting suspect Ahmad Al Aliwi Alissa (Boulder Police Dept.)

Among the victims was Boulder police officer Eric Talley, 51, who joined the department in 2010. Boulder Police Chief Maris Herold told reporters that Talley was the first to arrive after a call about shots being fired and someone carrying a rifle. 

Talley was "by all accounts, one of the outstanding officers" in the department, Boulder County District Attorney Michael Dougherty said. 

Boulder Police Officer Eric Talley was among the ten killed Monday during a mass shooting in Boulder, Colo. (Boulder Police Department)

Investigators have not established a motive, but they believe Alissa was the only shooter, Boulder County District Attorney Michael Dougherty said.

The attack was the nation's deadliest mass shooting since a 2019 assault on a Walmart in El Paso, Texas, where a gunman killed 22 people in a rampage that police said targeted Mexicans.

Supermarket employees told investigators that Alissa shot an elderly man multiple times outside the Boulder grocery store before going inside, according to the affidavit. Another person was found shot in a vehicle next to a car registered to the suspect's brother.

The gunfire sent terrorized shoppers and employees scrambling for cover. SWAT officers carrying ballistic shields slowly approached the store while others escorted frightened people away from the building, which had some of its windows shattered. Customers and employees fled through a back loading dock to safety. Others took refuge in nearby shops.

Monday's attack was the seventh mass killing this year in the U.S., following the March 16 shooting  that left eight people dead at three Atlanta-area massage businesses.

It follows a lull in mass killings during the coronavirus pandemic in 2020, which had the smallest number of such attacks in eight years, according to the database, which tracks mass killings defined as four or more dead, not including the shooter.

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Biden announced that flags nationwide would be lowered in memory of the victims — an order that comes just as a previous flag-lowering proclamation expired for those killed in the Atlanta-area shootings. Together the two orders mean near-continuous national mourning for almost two weeks.

The Associated Press contributed to this report.