Anders Behring Breivik is the admitted perpetrator of the July 2011 attacks in Norway that killed 77 people.
1979-
Student Seung-Hui Cho shot and killed 30 people on Virginia Tech's campus in 2007. The mass murder ended when he turned the gun and shot himself in the head.
1984-2007
1971-
Pretty Boy Floyd is best known for his constant run-ins with police and violent bank robberies.
1904-1934
In 1966, Thomas Watt Hamilton attacked a classroom at the Dunblane Primary School in Scotland.
1952-1996
Mass murderer Eric Harris and his friend Dylan Klebold killed themselves, 13 people and wounded more than 20 others at Columbine High School on April 20, 1999.
1981-1999
Andrew Kehoe was a mass murderer who went on a 1927 killing spree that included dynamiting the Bath, Michigan Consolidated School, killing 37 children.
1872-1927
Along with Eric Harris, Dylan Klebold shot and killed 13 people and injured 20 at Columbine High School on April 20, 1999.
1981-1999
Adam Lanza shot and killed 20 first-graders and six adults at Sandy Elementary School in Newtown, Connecticut, on December 14, 2012, before shooting himself.
1992-2012
Marc Lepine went on a shooting spree in 1989 that became known as the Montreal Massacre, which killed 14 people.
1964-1989
Lee Boyd Malvo was one of the vicious snipers who bred fear in the Washington, D.C. area for more than 20 days in 2002.
1985-
1967-
John Allen Muhammad became an infamous figure as part of a sniper team that terrorized the Washington, DC, area for several weeks in October 2002
1960-2009
In 1966, Richard Speck committed one of the most horrifying mass murders in American history when he brutalized and killed eight student nurses living on Chicago's South Side.
1941-1991
After murdering a gas station attendant in 1957, Nebraska native Charles Starkweather embarked on a murderous rampage with girlfriend Caril Ann Fugate in 1958. Together, they killed 10 people.
1938-1959
Charles Whitman was a former Marine and sniper who killed 16 people at the University of Texas in 1966.
1941-1966