THE worst in a long history of shootings at US schools and colleges was the 2007 Virginia Tech massacre when gunman Seung-Hui Cho killed 32 people and wounded 25 others before killing himself.
In 1970, four students were killed and nine wounded by National Guard troops dealing with anti-war protests on the campus of Kent State University in Ohio.
In 1991, Gang Lu, a graduate student in physics from China, apparently upset because he was passed over for an academic honour, opened fire in two buildings on the University of Iowa campus. Five people were killed before the 28-year-old turned his weapon on himself.
In 1999, 12 students and a teacher were murdered at Columbine High School in Colorado by two boys who then killed themselves.
And in an apparent murder-suicide in 2000, James Easton Kelly, 36, a University of Arkansas graduate student who had been dropped from a doctoral programme, and John Locke, 67, the professor overseeing his course work, were shot dead.
In 2002, failing University of Arizona nursing student Robert Flores, 40, killed a female instructor in her office.
Minutes later, armed with five guns, the Gulf War veteran entered one of his nursing classrooms and killed two more instructors before killing himself.