Here is what we know about the mass shooting in Boulder, Colorado, that left 10 dead

Ten people, including a Boulder police officer and a store manager, were killed Monday when a gunman attacked a King Soopers supermarket in Colorado.

A suspect is in custody, but the motivation behind the massacre still isn’t known, authorities say. Here is what we know so far:

What happened?

Police said they were called to the King Soopers store over reports of gunfire around 2:40 p.m. MDT Monday.

A man wearing a “tactical” or “armored” vest opened fire, killing people in the parking lot and inside the store, according to a court document released by Boulder County officials the next day.

A witness, Anna Haynes, said she was in an apartment across the street and heard gunshots. When she looked out her window, she “saw a body in the middle of the parking lot,” the University of Colorado Boulder student told CNN.

Haynes said she then saw a gunman “shooting rapid-fire” at something before he entered the building. Then, she saw people running outside.

Police and ambulances arrived. Shortly after the first calls, officers radioed that they were in a gunfight, according to audio from scanner traffic. They they were being fired at with multiple rounds through at least 3:21 p.m. local time.

A suspect was taken into custody at 3:28 p.m., police Chief Maris Herold said.

At one point, police were seen moving on the roof of the store. The reason for the movements was unclear, but one witness told CNN affiliate KCNC that his relatives in the store were evacuated through the roof.

Who are the victims?

Boulder police Officer Eric Talley, 51, was killed, having been one of the first officers to respond to the scene, Chief Herold said.

Also killed were Denny Stong, 20; Neven Stanisic, 23; Rikki Olds, 25; Tralona Bartkowiak, 49; Suzanne Fountain, 59; Teri Leiker, 51; Kevin Mahoney, 61; Lynn Murray, 62; and Jody Waters, 65, police said Tuesday.

Talley, a father of seven children ages 5-18, once had a different profession and “didn’t have to go into policing, but he felt a higher calling,” Herold said.

“He cared about this community … and he was willing to die to protect others,” she said.

Olds, 25, of Lafayette, was a front-end manager at the store, her uncle, Bob Olds, told CNN.

She was a “strong, independent young woman” who was raised by her grandparents, Bob Olds said. “She was so energetic and charismatic and she was a shining light in this dark world,” he told CNN.

Who is the suspect?

Ahmad Al Aliwi Alissa, 21, of the Denver suburb of Arvada, was taken into custody at the shooting site, accused of killing the 10, police said.

Alissa was shot at some point in the leg. Officers had exchanged gunfire with him at the store, but it wasn’t clear who shot him, Herold said.

He was treated for his injury at a hospital, but by Tuesday he had been booked into a county jail on 10 counts of murder in the first degree, police said.

Investigators don’t have information about a motive. Still, they believe he was the only perpetrator, authorities said at a news conference Tuesday.

The suspect has “lived most of his life in the United States,” Boulder County District Attorney Michael Dougherty said, without elaborating.

“In terms of statements that he (Alissa) may have made to investigators … we’re collecting those statements now, and we’ll be providing those in the weeks ahead,” Dougherty said.

An AR-15-style pistol that had been modified with an arm brace was used in the shooting, a senior law enforcement source told CNN on condition of anonymity. A search of the suspect’s home turned up other weapons, the source said.

Images from the scene on Monday — from a livestreamer and from CNN affiliate KMGH — showed police escorting from the building a shirtless man with blood on his leg, with his hands apparently cuffed.

That man was the arrested suspect, Ahmad Al Aliwi Alissa, his brother, Ali Aliwi Alissa, told CNN.

Where does the investigation go next?

Police will be on the scene day and night to learn more about the violence that took place at the store, officials said.

“We will work around the clock to get this accomplished,” Herold said.

The killings come less than a week after three spa shootings in Atlanta, in which eight people were killed.

In the last week, the United States has had at least seven shootings in which at least four people were injured or killed.