According to a probable cause affidavit attained by CBS affiliate KDKA, Vice Principal Samuel King, overheard Alex Hribal say, "No, I am not dropping them (knives), my work is not done I have more people to kill," after he was detained by a school security guard.
This new information led police to upgrade 16-year-old Hribal's charges to 21 counts of attempted homicide. Investigators say they also found a signed note in his locker from April 6, 2014 indicating that he planned to kill his fellow students.
"I can't wait to see the priceless and helpless 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 among them that is a plebeian," read the note, according to the affidavit.
KDKA reports that this new information confirms investigator's suspicions that Hribal may have been targeting specific students. Earlier this month, investigators were looking into claims that students at the high school had received threatening phone message believed to be made from Hribal, including one where it's now believed he called someone saying he would "(expletive) them up" on the eve of the stabbing.
However, Hribal's attorney, Pat Thomassey, reportedly denies this claim, saying that the suspect was "home all night with his parents."
Hribal's spree left 20 students and a security guard wounded. Most of the victims have been treated and released from nearby hospitals.