Factbox: Major school shootings in the United States

The bloodshed was the latest outbreak of gun violence that has become a regular occurrence at U.S. schools and colleges.

Below are some of the worst U.S. school shootings in the last 20 years:

BENTON, Kentucky, Jan. 23, 2018 - A 15-year-old boy kills two fellow students, both also 15, at Marshall County High School in western Kentucky with a pistol and wounds 13 others. Authorities give no motive for the attack.

AZTEC, New Mexico, Dec. 7, 2017 - A 21-year-old man disguised as a student enters the local high school, kills two students and then shoots himself to death.

SAN BERNARDINO, California, April 10, 2017 - A man dies of a self-inflicted gunshot wound after killing his estranged wife at North Park Elementary School. An 8-year-old student is also shot to death.

ROSEBURG, Oregon, Oct. 1, 2015 - A man opens fire on the campus of Umpqua Community College, killing nine people before he is shot dead by police.

MARYSVILLE, Washington, Oct. 24, 2014 - A freshman at Marysville-Pilchuck High School fatally wounds four students in the cafeteria before killing himself.

SANTA MONICA, California, June 7, 2013 - A one-time digital media student fatally shoots his father and brother, sets their house on fire, and then kills three people at Santa Monica College. The gunman kills himself.

NEWTOWN, Connecticut, Dec. 14, 2012 - A man fatally shoots his mother, then kills 20 children and six adults before killing himself at Sandy Hook Elementary School.

OAKLAND, California, April 2, 2012 - A former nursing student kills seven people and wounds three at Oikos University, a Korean Christian college.

CHARDON, Ohio, Feb. 27, 2012 - Seventeen-year-old student at Chardon High School kills three students and wounds three in school cafeteria.

HUNTSVILLE, Alabama, Feb. 12, 2010 - A biology professor at the University of Alabama at Huntsville opens fire during a staff meeting, killing three faculty members and wounding three.

DEKALB, Illinois, Feb. 14, 2008 - A former graduate student kills five students and wounds 16 at Northern Illinois University before taking his own life.

BATON ROUGE, Louisiana, Feb. 8, 2008 - Nursing student at Louisiana Technical College kills two classmates and herself in a classroom.

BLACKSBURG, Virginia, April 16, 2007 - A gunman slaughters 32 people and kills himself at Virginia Polytechnic Institute and State University, popularly known as Virginia Tech.

NICKEL MINES, Pennsylvania, Oct. 2, 2006 - A gunman kills five girls in a one-room Amish schoolhouse, before killing himself.

SHEPHERDSTOWN, West Virginia, Sept. 2, 2006 - A 49-year-old man shoots himself and his two sons to death during a visit to the campus of Shepherd University.

RED LAKE INDIAN RESERVATION, Minnesota, March 21, 2005 - A 16-year-old high school student kills seven people and wounds several others in a shooting rampage after killing two people off campus. He then kills himself.

COLD SPRING, Minnesota, Sept. 24, 2003 - Fifteen-year-old student fatally shoots a freshman and a senior at Rocori High School.

TUCSON, Arizona, Oct. 29, 2002 - A failing student shoots and kills three professors and then himself at the University of Arizona School of Nursing.

GRUNDY, Virginia, Jan. 16, 2002 - A recently dismissed graduate student kills a dean, a professor and a student at the Appalachian School of Law and wounds three others.

SANTEE, California, March 5, 2001 - A student at Santana High School kills two students, wounds 13.

LITTLETON, Colorado, April 20, 1999 - Two teenagers rampage through Columbine High School, fatally shooting 12 students and a teacher and wounding more than 20 others before killing themselves.

JONESBORO, Arkansas, March 24, 1998 - Two boys, ages 11 and 13, fire on their middle school from woods, killing four girls and a teacher and wounding 11 others.

(Compiled by Ian Simpson in Washington; Editing by Cynthia Osterman)