CENTENNIAL, Colo. (Reuters) - The teenage gunman who killed a classmate at a Colorado high school before taking his own life this month went bowling before the attack then drove to school and entered through a door that should have been locked, a sheriff disclosed on Monday.
Armed with a 12-gauge pump-action shotgun, a machete and three Molotov cocktails, 18-year-old Karl Pierson stormed Arapahoe High School in the Denver suburb of Centennial on December 13 in a rampage evoking comparisons to the far bloodier Columbine High School massacre that unfolded nearby in 1999.
Media reports have suggested the two young Columbine shooters also went bowling before committing the slayings, though whether they actually did remains uncertain.
The violence at Arapahoe High came on the eve of the one-year anniversary of the deadly shooting frenzy at Sandy Hook Elementary School in Newtown, Connecticut, where 20 children and six adults were killed by a gunman who then committed suicide.
Arapahoe County Sheriff Grayson Robinson told reporters on Monday that Pierson "made no attempt to conceal the fact that he was armed" and entered the school through a door that was supposed to be locked on the north side of the building.
"Unfortunately, it rarely is (locked) because it is more convenient for people to come and go from that area and not have to be obstructed by a locked door," Robinson said. "The door that he entered was not secured on December 13."
Asked if Pierson would have been thwarted in his attack had he found the door bolted shut, Robinson said it was unclear.
A representative for Littleton Public Schools, the district that runs Arapahoe High School, could not be reached for comment on Monday because their offices were closed for the holidays.
Pierson fired his shotgun several times inside the school and ignited one of his incendiary devices, sparking a small fire in the library.
Police have previously said Pierson was believed to have been motivated by a grudge against the school's librarian and debate coach, Tracy Murphy, who fled the building as Pierson was looking for him and escaped unhurt.
Claire Davis, 17, was shot in the face at point-blank range as she sat outside the library with a friend during the 80-second shooting spree, police said. Investigators concluded Pierson and Davis were acquaintances, but there was no evidence that he sought her out before shooting her.
Davis, a popular senior and accomplished equestrian, was the only person hit by gunfire in the rampage, and died at a local hospital on December 22 with her family at her side. She had been in a coma since the shooting.
Pierson committed suicide with the shotgun inside the library as an armed deputy stationed at the school closed in on him, police said.
The shooting occurred 8 miles from Columbine, where two heavily armed teenagers, also carrying homemade incendiary bombs, shot dead a teacher and 12 fellow students before committing suicide.
In an indication that he might have taken inspiration from the Columbine attack, Pierson went bowling alone in the morning before committing the attack at Arapahoe High School, the sheriff said. Robinson did not say what bowling lanes Pierson had visited or for how long he played.
Authorities have previously disclosed that the dozens of rounds of ammunition Pierson carried into the school were purchased by him that morning. He bought the shotgun on December 6.
If Pierson did take a cue from the Columbine killings, he would not be alone among school shooters.
A Connecticut state's attorney report released last month on the December 14, 2012, shooting rampage at Sandy Hook Elementary School described 20-year-old gunman Adam Lanza's "obsession" with the Columbine shootings.
Pierson had written on his arm five locations in the 2,000-student school, and also the Latin phrase, "Alea iacta est," which translates into English as "The die has been cast," police previously revealed.