What motivated a stabbing rampage at a Pennsylvania high school remains a mystery, with the teenage suspect's attorney calling him a good student who got along with others.

Sixteen-year-old Alex Hribal (RY'-buhl) faces dozens of charges, including four counts of attempted homicide, in the stabbing attack that injured 21 students and a security guard at Franklin Regional High School outside Pittsburgh. He's jailed without bail.

Police say Hribal used two kitchen knives to attack students up and down a hallway. At least five students were critically wounded, including a boy who was on a ventilator after a knife pierced his liver.

Students say Hribal was quiet and shy and largely kept to himself.

Defense attorney Patrick Thomassey has asked for a psychiatric examination.