A mass stabbing has occurred at a Pittsburgh-area high school, injuring 20 people on Wednesday morning. A 16-year-old sophomore has been identified as the suspect, causing life-threatening injuries to some.

The stabbing took place at Franklin Regional High School in Murraysville, Pa. The suspect, now in custody and being treated for hand injuries, hurt 19 students and one security guard in his rampage.

Dan Stevens, spokesman for Westmoreland County Emergency Management, confirmed four people had such severe injuries they had to be flown by helicopter to local hospitals. In total, eleven victims were taken to four different area hospitals, CNN reports. The students injured range from aged 14 to 17 years old.

Murrysville police Chief Thomas Seefeld told KDKA, “The juvenile went down the hallway and was flashing two knives around and injured the people.”

A motive for the stabbings has not been identified just yet, but Seefeld did confirm they were looking into reports that the suspect had threatened another student during a phone call on Tuesday night.

Someone pulled the fire alarm when the suspect started on his rampage, which helped potential victims evacuate the school district and get out of harms way.