Alex Hribal, 16, is now charged with 21 counts of attempted homicide, up from four. One of the victims was a security guard. Police said the signed note found in Hribal's locker was dated April 6, three days before the rampage at Franklin Regional High School near Pittsburgh.
According to the criminal complaint assistant, vice principal Samuel King grabbed Hribal in the bloody hallway and took him to the floor.
Hribal allegedly refused to drop the two knives he was carrying and said, "No, I am not dropping them, my work is not done, I have more people to kill," King said.
A search of Hribal's locker also turned up the April 6 note, which read in part, "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 isn't a plebian."
Hribal's attorney Patrick Thomassey did not immediately respond to a request for comment.
Two students remain hospitalized.