SHARE 2 4 COMMENTMORE

Two teens were injured Friday during a shooting at a suburban Denver high school by a fellow student, who then took his own life.

He has been identified as Karl Halverson Pierson.

The shooting - on the eve of the anniversary of the Newtown school massacre in which 20 students and six staffers were murdered - sent scores of terrified students and staffers at Centennial's Arapahoe High School scurrying at about 12:30 p.m. Police and other first responders quickly mobilized to surround the 2,220 student school.

One teen, believed to be 15 or 16, was hospitalized with a gunshot wound and listed in serious condition. Another student was also wounded by gunfire but not believed to be seriously injured. A third student was taken to the hospital to be treated for an anxiety attack.

Pierson, age 18, died of a self-inflicted gunshot, Arapahoe County Sheriff Grayson Robinson said. The incident unfolded when Pierson said he was interested in confronting a specific teacher. The teacher, informed of the situation, fled school unharmed, Robinson said.

"The youth who was hospitalized was shot after confronting the shooter," Robinson said. "The second student was found after police were clearing the school. He has a minor injury. "

Many students locked themselves in classrooms until first responders arrived. Some said they heard at least three gunshots in a hallway near the school library.

"We were shaking, we were crying, we were freaking out,'' 9th grader Whitney Riley told CNN.

Following the shooting, scores of students were seen calmly exiting the building single file with their hands above their heads and gathering on a school track at about 1:30 p.m. Frightened parents were told to go to Shepherd of the Hills Lutheran Church where they were to reunite with their kids.

SHARE 2 4 COMMENTMORE