Perpetrator was 21-year-old Austrian citizen and former high school student. He had legal gun permit and no police record. Failed to finish school. Pipe bomb and suicide note found at his home. Video message to parents recorded. Motive unknown. Killed himself in school toilet. Victims on multiple floors and outside building. 10 dead: 15-17-year-old students, one teacher, perpetrator. 12 injured, 4 critical. 28 total hospitalized. Polish 17-year-old only foreigner among victims. 300 police responded. Austria declared 3-day national mourning. President called victims young people with lives ahead. Largest tragedy in Austria recently.