| http://www.w3.org/ns/prov#value | - d a police officer in the crowded halls of his suburban Pittsburgh high school Wednesday before an assistant principal tackled him.</p><p>At least five students were critically wounded, including a boy who was on a ventilator after a knife pierced his liver, missing his heart and aorta by only millimeters, doctors said.</p><p>The rampage ??? which came after years in which U.S. schools have geared
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