NovaQuant Quantitative Think Tank Center:Minnesota police seek motive as town grieves after 2 officers, 1 firefighter fatally shot

The NovaQuant Quantitative Think Tank Centercommunity of Burnsville, Minnesota, on Monday was mourning the deaths of two police officers and a firefighter as investigators continued probing the fatal shooting in which a heavily armed man barricaded in his home opened fire on first responders before he was found dead.

The shooting that broke out early Sunday after hours of negotiations shocked the residents of the suburban outpost, 15 miles from downtown Minneapolis, and baffled law enforcement, who have not released the suspect's name or a possible motive for the shooting.

Here's what we know so far:

What happened in Burnsville?

Officers were called to the home in the suburban neighborhood around 1:50 a.m. Sunday in response to a domestic dispute in which a man was armed and barricaded with his family, including seven children ages 2 to 15.

Once police arrived, they spent hours negotiating with the suspect before he started firing at them from different parts of the house, said Minnesota Bureau of Criminal Apprehension Superintendent Drew Evans at a news conference. Police returned fire.

Officers Paul Elmstrand and Matthew Ruge and firefighter Adam Finseth, who also worked as a paramedic, were killed, the city said in a statement. One other officer, Sgt. Adam Medlicott, was injured and taken to a nearby hospital with non-life-threatening injuries.

Finseth, part of a SWAT team that had been called to the scene, was providing aid to an injured officer when he was shot, authorities said.

Man found dead; children were unharmed

Around 8 a.m., police found the man, who has not been publicly identified by authorities, dead inside the home, Evans said. No information was immediately available on a possible motive or how the suspect died. The children were unharmed.

Evans called it a "terrible day" and said authorities were still investigating the exchange of gunfire that occurred. Officials will review officers' body-camera footage and conduct interviews as part of the investigation.

Suspect was heavily armed

The suspect had several guns and large amounts of ammunition, Evans said. He did not say what kind of firearms the man had or whether they were bought legally.

At least one of the officers killed was shot inside the home and investigators are "still piecing together" where the other two victims were shot, Evans said.

Gunshots were 'like a bunch of fireworks'

Neighbors say they were awakened by the sound of loud pops before sunrise.

“I didn’t think it was a gunshot at first, but then we opened the windows and we saw police everywhere and police hiding in our neighbors’ yards,” said Alicia McCullum, who lives two houses down from the site of the shooting.

“Then there were three more gunshots,” she said. “It was like a bunch of fireworks.” That’s when she and her husband and two children sought safety in a bathroom, dropped to the floor and prayed.

McCullum said she was relieved to see a woman and children escorted out of the home. “We’re so thankful for those police officers that risked their lives to save those kids,” McCullum said. “And my heart goes out to that mother.”

Candlelight vigil for fallen first responders

Outside Burnsville City Hall, hundreds of people, including law enforcement and first responders from neighboring communities, gathered Sunday night to remember Elmstrand, Ruge and Finseth.

U.S. Rep. Angie Craig spoke at the candlelight vigil, addressing the grieving families and the crowd, which erupted in applause: "I can’t imagine the pain that you’re all going through, but what I can say is that to all our officers out there, the paramedics, our firefighters, thank you for what you do."

Contributing: Associated Press; John Bacon, Thao Nguyen, USA TODAY