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A student flashing two knives went on a stabbing rampage through the classrooms and halls of a high school outside Pittsburgh on Wednesday morning, authorities said. At least 19 students and a security guard were hurt, some with life-threatening injuries.

The suspect, a 16-year-old sophomore, was in custody and being questioned by police, authorities said. His motive was unclear, said Dan Stevens, a Westmoreland County emergency management spokesman.

The first photo of the suspect, above, emerged several hours after the mayhem. NBC News is blurring the face of the teen in the photo, from the Pittsburgh Tribune-Review, because of his age. He has not been charged or identified.