MURRYSVILLE, Pennsylvania (CNN) -- High schooler Mia Meixner was tending to her locker at the start of her day, when a ruckus behind her got her attention. Nothing to worry about, she thought -- until she saw one of them lift his shirt, and blood gushed out of his stomach. In the next five minutes, the boy went from classroom to classroom at Franklin Regional Senior High School, swinging two kitchen knives.