HIGHLANDS RANCH, Colo. - The DenverChannel CALL7 Investigators have identified Karl Pierson as the Arapahoe High School student gunman who shot two students inside the school while seeking "revenge" on a staff member.
He went into the school armed with a shotgun looking for the school's librarian, Tracy Murphy -- who was head of the school's debate team and who had recently kicked Pierson off the team, sources told the CALL7 Investigators.
"We were just in the library doing some work and we heard a loud bang. I thought it might have been someone dropping something, but then I heard two more," said senior Max Minne. "I knew it was a gun for sure."
Minne said he started to approach the front door of the library to see what was happening.
"The shooter just ripped through the door, started yelling 'Where's Murphy?' -- That's the main librarian of the school. I saw him bust through the door of the library with a gun, so I just took off and started yelling, 'Everyone get out! Everyone get out!'"
Minne said he ran out of the library through a back door with other students. It led them through a classroom and into the hallway near the west entrance.
The hallway, Minne said, was filled with smoke.
"There was a girl on the ground and she was bleeding out of her stomach -- at least that's what I thought it was. I was sprinting so fast that I didn't really get a look at her. She was on her knees," he said. "It was just tunnel vision; I was just trying to get out as quick as I can."
The 15-year-old girl who was shot was airlifted to Littleton Hospital, where she is listed in critical condition. Another student was also shot inside the school Friday, but has since been treated and released from the hospital.
The gunman was found dead from an apparent self-inflicted gunshot wound 5 minutes after the deputy made an initial radio call about the "active shooter" situation inside the school, Arapahoe County Sheriff Grayson Robinson said.
The faculty member -- Murphy -- escaped without injury.
7NEWS has learned that Pierson -- who was described as exceptionally bright but difficult and argumentative -- was upset about being booted from the debate team. Detectives are executing a search warrant at his Highlands Ranch home, looking for additional evidence.
They are also looking at his car and another home that he had temporary access to, Grayson said.