April 20, 1999: Columbine High School, Littleton, Colorado - Two students armed with guns, knives and bombs kill 12 students, one teacher and themselves.
April 16, 2007: Virginia Tech, Blacksburg, Virginia - A student kills 33 people in a shooting rampage on the campus before committing suicide.
Nov. 5, 2009: Fort Hood, Texas - A U.S. Army psychiatrist kills 13 people in a shooting spree. The assailant is currently being tried in a military court.
July 20, 2012: Aurora, Colorado - A gunman kills 12 people at a theater during the premier of the latest Batman movie before being arrested by police.