Some of the deadliest mass shootings that have taken place in the last three decades:
December 14, 2012: A total of 27 people are killed at a primary school in Newtown, Connecticut, in the northeastern United States, after a gunman opened fire. Twenty children and six adults were killed at the school, and another adult was killed at a second location. The gunman was also killed.
December 12, 2012: A gunman opens fire inside an Oregon shopping mall, killing at least two people before shooting himself to death.
August 14, 2012: A gunman shoots and kills a police officer and a civilian near a university in the US state of Texas, police said.
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 former graduate student at the University of Colorado, 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 fanatic admitted both attacks.
January 8, 2011: A gunman kills six people and wounds 13 others, including then-US Representative Gabrielle Giffords, in a shooting spree outside a grocery store in Tucson, Arizona. Doctors say Jared Lee Loughner, who has been charged in the deaths, suffers from schizophrenia.
November 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 Major Nidal Hasan is charged with 13 counts of premeditated murder and 32 counts of attempted premeditated murder.
April 30, 2009: Farda Gadyrov, 29, enters the prestigious Azerbaijan State Oil Academy in the capital, Baku, armed with an automatic pistol and clips. He kills 12 people before killing himself as police close in.
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, 18-year-old Pekka-Eric Auvinen fires kills eight people at his high school in Tuusula, Finland.
April 16, 2007: Seung-Hui Cho, 23, kills 32 people and himself on the Virginia Tech campus in Blacksburg, Virginia.
April 26, 2002: Robert Steinhaeuser, 19, who had been expelled from school in Erfurt, Germany, kills 13 teachers, two former classmates and policeman, before committing suicide.
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.
April 28, 1996: Martin Bryant, 29, bursts into cafeteria in seaside resort of Port Arthur in Tasmania, Australia, shooting 20 people to death. Driving away, he kills 15 others. He was captured and imprisoned.
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.
June 18, 1990: James Edward Pough shoots people at random in a General Motors Acceptance Corp. office in Jacksonville, Florida, killing 10 and wounding four, before killing himself.
December 6, 1989: Marc Lepine, 25, bursts into Montreal's Ecole Polytechnique college, shooting at women he encounters, killing nine and then himself.
August 19, 1987: Michael Ryan, 27, kills 16 people in small market town of Hungerford, England, and then shoots himself dead after being cornered by police.
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.
July 18, 1984: James Oliver Huberty, an out-of-work security guard, kills 21 people in a McDonald's restaurant in San Ysidro, California. A police sharpshooter kills Huberty.
July 12, 1976: Edward Charles Allaway, a custodian in the library of California State University, Fullerton, fatally shot seven fellow employees and wounded two others.