The teenager arrested after yesterday’s stabbing of 21 students and a security guard at a Pennsylvania high school has been charged as an adult. Suspect Alex Hribal, 16, was subdued by an assistant principal and the guard as he reportedly slashed at students with two kitchen knives up to 10 inches long. Four victims remain in critical condition. Hribal has been arraigned on four counts of attempted homicide, 21 counts of aggravated assault and one count of possessing a prohibited weapon on school property. Police haven’t yet determined a motive.