Jacki Kelley, spokesperson for the Jefferson County Sheriff's Office, says one victim was found inside at Deer Creek Middle School and the other was found outside the school.
Deer Creek is on West Columbine Drive near South Garrison Street, which is near Kipling Parkway and Ken Caryl Avenue.
The victims were a boy and a girl. Both were initially taken to Littleton Adventist Hospital with what authorities initially said were non life-threatening injuries.
Kelley says the shootings happened outside of the school around 3 p.m., which is about when children would be getting out of school.
One of the victims is a seventh-grade girl named Reagan Weber. She was treated and released from Littleton Adventist Hospital.
The other victim is an eighth-grade boy named Matt Thieu. He transferred to The Children's Hospital and is now listed in critical condition.
Kelley says both had surgery on Tuesday.
Kelley says deputies took 32-year-old Bruco Strong Eagle Eastwood into custody and he is being held at the Jefferson County Sheriff's Office. He is expected to face at least two counts of attempted first-degree murder and will appear in court at 10 a.m. on Wednesday for an advisement hearing.
His picture was not released pending a photo lineup.
Kelley says two people tackled Eastwood to the ground and a contractor pulled the gun away from him.
"There's no reason for us to believe that these two victims were targeted. It may have really been happenstance," Kelley said. "It could have been so much worse."
She says there are reports Eastwood was at the school prior to Tuesday.
"He was also briefly in the school today [before the shootings], although the shootings occurred outside," Kelley said.
Authorities say Eastwood used a bolt-action, high-powered rifle. 9Wants to Know has learned he has a lengthy criminal history of charges, including assault, domestic violence and DUI.
Kelley says authorities do not yet have a motive for the shootings.
Reese Ferrin, a Deer Creek student, says he was standing next to Dr. David Benke, a seventh-grade math teacher, when the shootings began. (Click here to read more about Benke.)
"I was by the crosswalk and the gunman came around the corner and Dr. Benke ran and tackled him," Reese said.
Reese says Benke tackled the gunman first and other teachers piled on top of him.
Benke's wife, Sandra Benke, told 9NEWS he called her just after the shooting.
"He wanted me to know, first of all that he was OK. That there'd been a shooting at the school and that he'd had to tackle the gunman and before he was able to get the gunman down he got a shot off and shot one of the students," she said.
"I'm not surprised that David would tackle somebody like that. He's 6'5" and he knows how to handle himself. He dearly loves his students. They're like an extended portion of his family. But I was really, really worried and glad to hear that he was OK," she said.
One student says she spoke with the shooter and he asked some students if they went to school at Deer Creek before he opened fire.
Sheri Hasse says her son was on the bus and he saw at least one of the shootings happen outside the school. Her son was kept on the bus as deputies investigated the scene.
Thirteen-year-old Kyle Barker was also on the bus and says they heard the first shot and everyone on the bus got down. He says he peeked up and saw students running away from the gunman around the back of the bus. He says one of those kids was the second victim. He watched the student fall to the ground after being shot. He says he also saw teachers tackling the gunman and one teacher came over and put a coat over the victim. They didn't do CPR, but did apply pressure to the wound.
Levi Shafter, a seventh grader, was also on the bus.
"I heard a gunshot and everybody was running away, I was a little confused, and then I saw the shooter, I saw him put out a second shot and that's when the bus driver told us all to get down so we got down," Levi said. "I was really scared."
"Some of the teachers tackled him and then the police arrived and arrested him," Levi said.
Tamara Vermeer has a daughter who is an eighth grader at Deer Creek. She says she was parked close to the front of the school and heard a gunshot.
"At that time, of course, I'm not thinking it's a gunshot. I see my daughter and her friends coming towards me and I hear a second gunshot and all - probably nine or 10 of them, just piled in my car and then I saw kids starting to run," she said.
"I could see adults or someone leaning over someone," Veremeer said. "And then I saw a woman come out and pick up a rifle and so that's when I knew this was a shooting."
Kelley says Deer Creek was put into lockdown because of the shooting.
All of the students were taken to nearby Stony Creek Elementary School at West Columbine Drive and South Everett Street. Parents were told to go to Stony Creek to pick up their children.
Groups of children were sent from one school to the other as investigators cleared Deer Creek.
Tuesday was not the first shooting on the Deer Creek campus. On April 7, 1982, 14-year-old Jason Rocha shot and killed a 13-year-old student named Scott Michael during a lunch-hour recess at the school.
The school is also about three miles southwest of Columbine High School, where two teens - Dylan Klebold and Eric Harris - killed 12 students and a teacher and wounded 23 others before killing themselves in 1999.
About 525 seventh and eighth grade students attend Deer Creek.
Jefferson County Schools says both Deer Creek and Stony Creek will be closed on Wednesday. Counselors will be available for anyone who needs them at Stony Creek beginning at 7:30 a.m. They will be there throughout the day.
All Jeffco activities, except athletics, were cancelled for Tuesday night. All athletic events were to go on as scheduled.
It is unclear when classes would resume at the schools, but parents can get updates at www.jeffcopublicschools.org or call 303-982-6600.
Click here to discuss the shootings on MomsLikeMe.com.
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