The former patient stabbed five people at the Turtle Creek Valley Mental Health facility in Munhall, Pa., according to an article on the Pittsburgh Press-Gazette website.
The assailant was armed with a knife and an air pistol, the article said.
County police also found two knives among his belongings and two more near where he fell after being shot.
The complaint said the attacker also poured an accelerant on the floor of an elevator in the building.