A gunman at a Connecticut elementary school killed 27 people, including 20 children on Friday. It is among the world's worst mass shootings.
Here is a look at some others:
- August 5, 2012. Army veteran Wade Michael Page kills five men and one woman and wounds three other people, including a police officer, before taking his own life at the Sikh Temple of Wisconsin outside Milwaukee.
- July 20, 2012. At least 12 people are killed when a gunman enters an Aurora, Colorado, movie theatre, releases a canister of gas and then opens fire during opening night of the Batman movie 'The Dark Knight Rises'. James Holmes, a 24-year-old, has been charged in the deaths.
- July 22, 2011. Confessed mass killer Anders Behring Breivik kills 77 in Norway in twin attacks: a bombing in downtown Oslo and a shooting massacre at a youth camp outside the capital. The self-styled anti-Muslim militant admitted both attacks.
- March 10, 2009. Michael McLendon (28) killed 10 people - including his mother, four other relatives, and the wife and child of a local sheriff's deputy - across two rural Alabama counties. He then killed himself.
- September 23, 2008. Matti Saari (22) walks into a vocational college in Kauhajoki, Finland, and opens fire, killing 10 people and burning their bodies with firebombs before shooting himself fatally in the head.
- November 7, 2007. After revealing plans for his attack in YouTube postings, Pekka-Eric Auvinen (18) fires kills eight people at his high school in Tuusula, Finland.
- April 20, 1999. Students Eric Harris (18) and Dylan Klebold (17) opened fire at Columbine High School in Littleton, Colorado, killing 12 classmates and a teacher and wounding 26 others before killing themselves in the school's library.
- March 13, 1996. Thomas Hamilton (43), kills 16 kindergarten children and their teacher in elementary school in Dunblane, Scotland, and then kills himself.
- October 16, 1991. A deadly shooting rampage took place in Killeen, Texas, as George Hennard opened fire at a Luby's Cafeteria, killing 23 people before taking his own life. 20 others were wounded in the attack.
- August 20, 1986. Pat Sherrill (44), a postal worker who was about to be fired, shoots 14 people at a post office in Edmond, Oklahoma. He then kills himself.