MURRYSVILLE, Pa. (AP) — A police chief says a 16-year-old boy “was flashing two knives around” when he injured 19 students and a school police officer who eventually subdued him with the help of an assistant principal at a high school near Pittsburgh.

Murrysville police Chief Thomas Seefeld says the bloody crime scene left behind Wednesday at Franklin Regional High School is “vast” and may take a couple of days to process.

Police haven’t named the suspect who was taken into custody but says he’s being treated for a minor hand wound.

Investigators haven’t determined a motive but say they’re looking into reports of a threatening phone call between the suspect and another student the night before.

At least two of the victims were in critical condition, though doctors expect all victims to survive.