It's possible that a third suspect remains in STEM School Highlands Ranch, which is still being searched, Douglas County Undersheriff Holly Nicholson-Kluth said at a news conference.
Authorities say a shooting at a suburban Denver school has injured two people.
Ms Nicholson-Kluth said police and deputies got there nearly immediately and heard shots as they arrived. Two suspects are in custody but the total number of victims is not yet clear. More than 500 of those students are elementary age.
She said she did not believe there were any other gunmen, but tactical teams were still searching the school room by room.
They described the situation as unstable and are directing parents to pick up their children at a nearby staging area.
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The STEM school has been placed in lockdown.
Concerned mother Kelley Paulson told KMGH that her sixth-grade son got out of the school but her third-grade daughter was still inside.
A first responder helicopter lifts off near STEM School Highlands Ranch. We are monitoring the situation in real time.
"I tried to run with my life but I'm out of breath", Christian said.
More information wasn't immediately available.
This is a developing story.