These are some of the worst school shootings in recent years:
September 23, 2008: Matti Saari, 22, killed nine fellow students and a teacher before shooting himself at a school in Kauhajoki, Finland.
February 14, 2008: Former student Steven Kazmierczak, 27, opens fire in a lecture hall at Northern Illinois University in DeKalb, fatally shooting five students and wounding 18 others before committing suicide.
November 7, 2007: Pekka-Eric Auvinen, 18, shoots and kills eight people and himself at a high school in Tuusula, Finland.
April 16, 2007: Cho Seung-Hui, 23, fatally shoots 32 people in a dorm and a classroom at Virginia Tech in Blacksburg, then kills himself in the deadliest mass shooting in modern US history.
November 20, 2006: Sebastian Bosse, 18, goes on a rampage at his former high school in Emsdetten, Germany, near the Dutch border, shooting and injuring four students and the school janitor. Police commandos later found Bosse dead.
April 26, 2002: Robert Steinhaeuser, 19, previously expelled from a school in Erfurt, Germany, kills 13 teachers, two former classmates and a policeman, before committing suicide.
April 20, 1999: Students Eric Harris and Dylan Klebold open fire at Columbine High School in Littleton, Colorado, killing 12 classmates and a teacher and wounding 26 others before committing suicide in the school's library.
March 13, 1996: Thomas Hamilton, 43, killed 16 nursery children and their teacher in Dunblane, then shot himself.