New details of Colorado high school shooting released The 18-year-old who fatally shot a fellow student at Arapahoe High School in Centennial, Colo. earlier this month entered the school through a door that was supposed to be locked and went bowling the night before he carried out his plan. Those disclosures were among the new details of the December 13 shooting released by authorities at a news conference Monday. Investigators believe that the shooter, Karl Pierson, acted alone and was targeting school librarian and debate team coach Tracy Murphy, who had thrown him off the team earlier in the semester. Murphy was unscathed, but Pierson did shoot fellow student Claire Davis at point-blank range before taking his own life. Davis died of her injuries on December 21. Arapahoe County Sheriff Grayson Robinson described the shooting as "very deliberate and planned" and called Pierson an "evil individual." Arapahoe County District Attorney George Brauchler said that Pierson legally purchased the 12-gauge shotgun used in the shooting. After making purchases related to the attack on the morning of December 12, Robinson said Pierson went bowling by himself that night. When Pierson arrived at the school the next afternoon, he entered through a door that should have been shut and locked, the sheriff said. However, that fact does not seem to have altered the investigators' theory that Pierson acted alone. It was also revealed the Pierson had 125 rounds of ammunition on him that day, as well as a machete and three Molotov cocktails.