A note investigators obtained from Alex Hribal's locker at Franklin Regional High School was titled "ragnorok," referring to the battle before the end of the world in Norse mythology.
"I can't wait to see the priceless and hopeless looks on the faces of the students of one of the 'best schools in Pennsylvania,' realize their precious lives are going to be taken by the only one of them that isn't a plebeian," Hribal wrote in the note, which was dated three days before the April 9 attack.
John Lindow, a professor at the University of California's Berkeley campus, told the Philadelphia Tribune-Review that ragnorok -- or ragnorak -- refers to a violent battle.
"Bonds disintegrate, order vanishes, the gods die fighting with their enemies and the world sinks into the sea," he said. "It then rises from the sea and a new world is born."
Hribal was charged with 21 counts of attempted homicide after allegedly using two kitchen knives to attack his fellow classmates. Assistant Principal Sam King stopped the attack by tackling Hribal to the ground.