The shooter who entered Arapahoe High School in Centennial, Colo., targeted five separate areas of the building and wrote, "The die has been cast," in Latin on his arm, an indication of his plan of attack, authorities said.
In a statement released Tuesday, Arapahoe County Sheriff Grayson Robinson gave new details on last week's violence at the school that left one girl in a coma in critical condition and the shooter, Karl Pierson, dead by his own hand.
According to the sheriff's office, Pierson, 18, entered the building on Friday with a 12-gauge shotgun, a machete, three functional incendiary devices and 125 rounds of ammunition. He opened fire as soon as he entered, hitting Claire Davis, 17, a fellow senior, who has been described as a bystander.
Using an indelible marker, Pierson wrote five separate letters and numbers on his arm, a guide to his plan of attack as he hunted his debate coach with whom he had a disagreement, the sheriff said. The teacher was also the school librarian.
"The letters/numbers written on the shooter's arm [are] an indicator to investigators of the shooter's plan," Robinson said in the statement.
But the sheriff also said investigators will explore whether Pierson had other victims in mind and will closely evaluate "if the occupants of those classrooms may have also been targeted for harm by the shooter."
On the inside of his arm, Pierson also wrote the Latin phrase, "Alea iacta est," which means, "The die has been cast," the sheriff's office said.
State investigators and the FBI have joined the probe, the sheriff said.