April 16, 2007: A gunman kills 21 people in a dorm and a classroom at Virginia Tech in Blacksburg, Va.
Sept. 2, 2006: Douglas W. Pennington, 49, kills himself and his two sons, Logan P. Pennington, 26, and Benjamin M. Pennington, 24, during a visit to the campus of Shepherd University in Shepherdstown, W.Va.
Oct. 28, 2002: Failing University of Arizona Nursing College student and Gulf War veteran Robert Flores, 40, walks into an instructor's office and fatally shoots her. A few minutes later, armed with five guns, he enters one of his nursing classrooms and kills two more of his instructors before fatally shooting himself.
Jan. 16, 2002: Graduate student Peter Odighizuwa, 42, recently dismissed from Virginia's Appalachian School of Law, returns to campus and kills the dean, a professor and a student before being tackled by students. The attack also wounds three female students.
Aug. 28, 2000: James Easton Kelly, 36, a University of Arkansas graduate student recently dropped from a doctoral program after a decade of study, and John Locke, 67, the English professor overseeing his coursework, are shot to death in an apparent murder-suicide.
Aug. 15, 1996: Frederick Martin Davidson, 36, a graduate engineering student at San Diego State, is defending his thesis before a faculty committee when he pulls out a handgun and kills three professors.
Nov. 1, 1991: Gang Lu, 28, a graduate student in physics from China, reportedly upset because he was passed over for an academic honor, opens fire in two buildings on the University of Iowa campus. Five University of Iowa employees are killed, including four members of the Physics Department; two other people are wounded. The student fatally shoots himself.
Aug. 1, 1966: Charles Whitman points a rifle from the observation deck of the University of Texas at Austin's Tower and begins shooting in a homicidal rampage that goes on for 96 minutes. Sixteen people are killed, including his wife and mother, who were shot the night before; 31 others are wounded.