CENTENNIAL, Colo. (CN) - A "nerdy, socially inept and clunky" teenager who shot to death a fellow student and took his own life at a Colorado high school last year acted alone, the sheriff's office said.
Karl Pierson entered Arapahoe High School through an unsecured door on Dec. 13, 2013, carrying a pump-action shotgun, hunting knife, three Molotov cocktails and backpack of ammunition, the Arapahoe County Sheriff's Office said in a 37-page report released on Oct. 10.
Pierson immediately fired on two female students, striking 17-year-old Claire Davis in the head and back. Davis died eight days later in a hospital.
After shooting Davis, Pierson ran to the school library, where he yelled for librarian Tracy Murphy by name. Pierson fired at Murphy, who escaped unharmed through a nearby door.
Pierson then set down the shotgun and lit and threw a Molotov cocktail, setting a bookcase and books on fire, according to the report. Students and staff scattered into the hallways or hid in closets.
Pierson, 18, was later found dead of a self-inflicted gunshot wound to the head, by a school resource officer and assisting deputies.
Arapahoe High was searched for other suspects and explosives. The school was cleared and evacuated without further incident.
Sheriff David Walcher said his office's report is based on 4,000 pages of documents, 200 interviews, 13 search warrants, 3 production of record requests, 200 evidence items, and 3,000 images and photos.
It also followed up numerous tips to the Sheriff's Office, review of 911 calls and surveillance video.
According to the report, librarian Murphy, who also coached the school's speech and debate team, once described Pierson as "nerdy, socially inept and clunky," but hoped he would "grow and develop self-confidence" through participation in the team.
Pierson, however, told students they were "stupid;" he was seen as "a verbal bully," the report states. He was "livid and threatening" and looked at Murphy with hatred, in a "haunting" way, upon being removed as the team's captain for his behavior, according to the report.
School officials said they had a bad "gut" feeling about Pierson, were concerned about him "snapping," and heard him threaten Murphy's life after his removal as captain, the report adds.
The report cites an except from Pierson's diary: "Sunday, Sept. 22, 2013, I am filled with hate. I love it. The serotonin supplements I am taking don't do jack shit, I am still ready to start a riot, I feel like a bomb, ready to let the world feel and experience my hatred for all things of pleasure. Nothing makes me happy. When I do commit my atrocities, I want the conversation to be about elementary school teasing. Words hurt, can mold a sociopath, and will lead someone a decade later to kill."
Walcher said the Colorado Bureau of Investigation confirmed that analysis of the shotgun, recovered in the library, showed it was capable of firing; that all recovered shells had been fired from the gun; and that shell shot size, trajectories and patterns of impact were consistent with the scene and witness statements.
Walcher added that, given there was no video from the school's library, information on the gun was "critical" to establish that Pierson acted alone.
"Inasmuch as there was no video from the library, this is critical to establish that no one else was involved in the planning and execution of the shooting and there was no other firearm used," Walcher said.
The Rocky Mountain Regional Computer Forensics Laboratory and FBI separately analyzed a computer tablet recovered from Pierson's home, Walcher said. The FBI found several photos of Pierson in the same clothing that he was wearing in the library, along with pictures of his gun, machete and ammunition.
"Related to both of these items, the shotgun and the tablet, I decided not to disclose the items and the reason for the delay in processing these items as it could have been detrimental to out investigation if anyone else was identified as being involved in the planning or execution of the shooting," Walcher said. "As it turned out, it is clear that no one else was involved."
Walcher said he understands that "many people" will want to review additional documents related to the investigation.
"For the most part, any documents related to this investigation are considered criminal justice records and we have a responsibility to thoroughly review those records before release," he added. "As I have states, the records associated with this investigation are voluminous; however, our Records staff and Attorney's Office are actively engaged in this process and we intend to make available any records that can be released once that review is complete."
Arapahoe County, pop. 572,003 in 2010, is named for the Arapaho Native American tribe who once lived in the region. It is Colorado's third-most populous county.
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