At least superficially, they appear to be coming more and more often.
From Reuters:
March 13, 1996 - BRITAIN - Gunman Thomas Hamilton burst into a primary school in the Scottish town of Dunblane and shot dead 16 children and their teacher before killing himself.
April 28, 1996 - AUSTRALIA - Martin Bryant unleashed modern Australia's worst mass murder when he shot dead 35 people at the Port Arthur tourist site in the southern state of Tasmania.
April 1999 - UNITED STATES - Two heavily-armed teenagers went on a rampage at Columbine High School in Littleton, Denver, shooting 13 students and staff before taking their own lives.
July 1999 - UNITED STATES - A gunman killed nine people at two brokerages in Atlanta, after apparently killing his wife and two children. He committed suicide five hours later.
June 2001 - NEPAL - Eight members of the Nepalese Royal family were killed in a palace massacre by Crown Prince Dipendra who later turned a gun on himself and died few days later. His youngest brother also died later raising the death toll to 10.
April 26, 2002 - GERMANY - In Erfurt, eastern Germany, 19-year-old Robert Steinhauser opened fire after saying he was not going to take a math test. He killed 12 teachers, a secretary, two pupils and a policeman at the Gutenberg Gymnasium, before killing himself.
Oct. 2002 - UNITED STATES - John Muhammad and Lee Malvo killed 10 people in sniper-style shooting deaths that terrorized the Washington, D.C., area.
April 16, 2007 - USA - Virginia Tech, a university in Blacksburg, Virginia, became the site of the deadliest rampage in U.S. history when a gunman killed 32 people and himself.
Nov. 7, 2007 - FINLAND - Pekka-Eric Auvinen killed six fellow students, the school nurse, the principal and himself with a handgun at the Jokela High School near Helsinki.
Sept. 23, 2008 - FINLAND - Student Matti Saari opened fire in a vocational school in Kauhajoki in northwest Finland, killing nine other students and one male staff member before killing himself.
March 11, 2009 - GERMANY - A 17-year-old gunman dressed in combat gear killed nine students and three teachers at a school near Stuttgart. He also killed one other person at a nearby clinic. He was later killed in a shoot-out with police. Two additional passers-by were killed and two policemen seriously injured, bringing the death toll to 16 including the gunman.
June 2, 2010 - BRITAIN - Gunman Derrick Bird opened fire on people in towns across the rural county of Cumbria. Twelve people were killed and 11 injured. Bird also killed himself.
April 9, 2011 - NETHERLANDS - Tristan van der Vlis opened fire in the Ridderhof mall in Alphen aan den Rijn, south of Amsterdam, killing six before turning the gun on himself.
July 22, 2011 - NORWAY - Police seize a gunman who killed 69 people at a youth summer camp of Norway's ruling political party, on the small, holiday island of Utoeya. Anders Behring Breivik is later charged with the killings, as well as with an earlier bombing in Oslo which killed eight people. The trial ended last month with Breivik saying that his bombing and shooting rampage was necessary to defend the country - prompting a walk-out by relatives of his victims.
Dec. 13, 2011 - BELGIUM - Gunman Nordine Armani killed three people, including a 17-month-old toddler, wounding 121 in a central square in the eastern city of Liege, before shooting himself. The next day Belgian investigators found the body of a woman in warehouse used by the gunman raising the death toll, including the killer, to five.
July 20, 2012 - UNITED STATES - A masked gunman killed 14 people and wounded 50 others when he opened fire on moviegoers at a showing of new Batman film "The Dark Knight Rises" in the city of Denver.