Officials: Arapahoe shooter planned to attack at least five areas of the school This Sept. 7, 2013 photo shows Arapahoe High School senior Karl Pierson as he poses for his class picture in Centennial, Colo. Pierson shot fellow student Claire Davis at the school on Friday, Dec. 13, 2013, before killing himself.&nbsp; Mary McGregor, AP More details have been released from the Arapahoe County Sheriff's Office following last week's school shooting in Arapahoe, Colo. Arapahoe County Sheriff Grayson Robinson had previously said Friday's shooting at Arapahoe High School by 18-year-old Karl Pierson was likely motivated by retaliation against librarian and debate coach Tracy Murphy, who had disciplined Pierson from the debate team. The teenager was unable to find Murphy but gravely wounded a fellow student, 17-year-old Claire Esther Davis, who remains in a coma at Littleton Hospital, before killing himself in the school's media center as police moved in. However, it now seems Pierson was planning to attack several areas of the school. Investigators discovered letters and numbers written on Pierson's body that correlate directly with specific classrooms located near the school's library. Investigators are trying to determine the relevance of the numbers written on Pierson's arm, while evaluating if the occupants of those classrooms may have also been targeted by the teenager. Pierson had also used an indelible marker to write a phrase in Latin on the inside of his forearm. The Latin phrase is "Alea iacta est," translates to English as "The Die Has Been Cast." Pierson entered the school armed with a .12 gauge pump action shotgun, making no effort to conceal the weapon. In addition to the shotgun, Pierson had also brought three molotov cocktails, a machete and more than 125 rounds of assorted types of shotgun ammunition into the school. He carried numerous rounds of shotgun ammunition in two bandoliers across his chest and waist, while the remaining were carried in a backpack. It still appears that Pierson acted alone, according to the sheriff.