A gunman at a Connecticut elementary school killed more than two dozen people, including children, on Friday. It is among the world's worst mass shootings. Here is a look at some others:

— July 20, 2012: Twelve people are killed when a gunman enters an Aurora, Colo., movie theater, 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 former graduate student at the University of Colorado, has been charged in the deaths.

— March 11, 2012: Sixteen Afghan villagers, including nine children, are killed during a predawn attack in which Army prosecutors have charged Staff Sgt. Robert Bales, 39.

— 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.

— Jan. 8, 2011: A gunman kills six people and wounds 13 others, including then-U.S. Rep. Gabrielle Giffords, in a shooting spree outside a grocery store in Tucson, Ariz. Doctors say Jared Lee Loughner, who has been sentenced to life in prison, suffers from schizophrenia.

— Aug. 3, 2010: Omar Thornton shot 10 people, eight of them fatally, within three minutes at the Hartford Distributors warehouse in Manchester, Conn., before killing himself in what was the worst mass shooting in Connecticut before Friday's school shootings in Newtown.

— Nov. 5, 2009: Thirteen soldiers and civilians were killed and more than two dozen wounded when a gunman walked into the Soldier Readiness Processing Center at Fort Hood, Texas, and opened fire. Army psychiatrist Maj. Nidal Hasan has been charged with 13 counts of premeditated murder and 32 counts of attempted premeditated murder.

— April 3, 2009: A 41-year-old man opened fire at an immigrant community center in Binghamton, N.Y., killing 11 immigrants and two workers. Jiverly Wong, a Vietnamese immigrant and a former student at the center, killed himself as police rushed to the scene.

— April 16, 2007: Seung-Hui Cho, 23, kills 32 people and himself on Virginia Tech campus in Blacksburg, Va.

— Sept. 27, 2001: A 57-year-old Swiss man armed with weapons including a SIG-Sauer pistol and an assault rifle killed 14 people in a cantonal parliament building in the Swiss city of Zug. Friedrich Leibacher killed himself following the shootings, which also wounded 18 others. Leibacher had been angry over perceived mistreatment by government officials. Continued...