Pierson fired one random round down a hallway and then went into the personal space of the female victim (17 year old senior Claire Davis) and shot her point blank. There was no interaction between them. She didn't have time to run.
He then fired another shot down a hallway and went into the library, where he fired another shot. After this fourth shot, he ignited one of the devices in the library, resulting in fire and smoke. Three bookshelves caught fire inside library
He fired a 5th time, ran to back to library and took his own life
The time span from his entering the school to his taking his own life was less than 1 minute and 20 seconds.
A deputy sheriff assigned to the school and a school resource officer were in the cafeteria and immediately aware there was a problem in the north side library. They ran from the cafeteria to the library, which is down a long hallway. The deputy was yelling at people in the library to get down and identified himself as a deputy Arapahoe County sheriff. The Sheriff today said Pierson knew the deputy was there and was going to contain him. Because experts say the typical shooter will shoot until confronted by someone in position of authority, the Sheriff says he is convinced that it was the quick arrival of the deputy that caused Pierson to kill himself and prevented more carnage.
Pierson purchased the pump shotgun legally on December 6 from a local retail store. Yesterday morning he purchased ammunition, also legally, before going to the school.
In Colorado, 18 year olds can purchase shotguns but not handguns.
Claire Ester Davis, the senior who was shot, has severe head trauma. She remains in critical condition following yesterday's surgery.
Claire is an accomplished equestrian. Her family asks the community to pray for her. In March, she came in first in the Col. R.L. Robertson Medal Entries, riding her horse Graphite Gran Grannus. Here's a list of her placements. (According to the Denver stock show, her mom owns Grannus.)
The apparent motive continues to be retaliation against the librarian Tracy Murphy, who also led the debate team. The Sheriff says Pierson was not suspended from school and he was not dismissed from the debate team. He's not aware of prior disciplinary action against Pierson.
The Sheriff, who seems to be a pretty accomplished speaker (no rambling, no notes, logical presentation) spent almost as much time praising law enforcement as he did explaining what happened.
Some quick thoughts: This version does not exactly match the account of the janitor (more versions here, here and here) or at least two students who gave video interviews to the media. The janitor said he was outside the north entrance and saw Pierson enter. He then heard 2 pops and called for help. He said the librarian ran out and a bullet whizzed by the librarian's head and he escorted him to his (the janitor's) truck and they drove across the street where the librarian told him what happened.
A student named Frank who was a friend of Pierson's said he was returning from having lunch off-site and saw the libarian run out and he talked to the teacher. The librarian told him what happened saying over and over it was Pierson. Another student said he saw Claire Davis bleeding profusely from the stomach (not the head.)
If Pierson bought the gun Dec. 6, it seems that whatever went down between him and Murphy happened last week, not this week.
As to those blasting Pierson for his "liberal" or "socialist" politics and blaming his parents for them, according to Lexis Nexis, his parents, Charles Pierson and Barbara Halverson Pierson, are both long-time registered Republicans.