Sources say close to 30 people were killed, many of whom were children, during a school shooting the Sandy Hook Elementary School in Newton, Conn.
A man opened fire at the Clackamas Town Center mall in Oregon Tuesday, leaving three dead, including the shooter, according to a spokesman from the Clackamas County Sheriff's Office.Take a look at some of the worst mass shootings in U.S. history.
A man who apparently had just lost his job at a small business in Minneapolis returned to the building Sept. 27 and opened fire, killing the company's founder and three others and wounding four others before taking his own life.
August's Empire State Building shooting left two people dead and several others wounded.
July 20, 2012: James Holmes is accused of opening fire in an Aurora, Colo., movie theater, killing at least 12 and wounding 58 others.
Jan. 8, 2011: Jared Lee Loughner killed six and wounded 13, including then-Rep. Gabrielle Giffords, outside a grocery store in Tucson, Ariz. Loughner pleaded guilty in 2012 and was sentenced to life in prison without the possibility of parole.
Nov. 5, 2009: Major Nidal Hasan, a psychologist with the U.S. Army, killed 13 soldiers and wounded 32 others at Fort Hood, Texas. Hasan was convicted of 13 counts of murder and 32 counts of attempted murder, and a military jury has recommended the death penalty.
April 3, 2009: Gunman Jiverly Wong, 42, burst into a citizenship class at an immigration center in Binghamton, N.Y., killing 13 and wounding four before killing himself.
March 30, 2009: A gunman shot eight people to death and wounded several others at a nursing home in North Carolina. Most of those killed were elderly nursing home patients.
March 29, 2009: A gunman killed five family members, including his two children, and wounded his wife at a townhome in Santa Clara, Calif., before killing himself.
March 10, 2009: Michael McLendon, 28, is accused of killing 10 people in several towns in Alabama before killing himself. The dead included several family members, including his mother and grandparents.
Dec. 24, 2008: Bruce Jeffrey Pardo, 45, dressed up in a Santa suit and showed up at a Christmas party at his ex-wife’s parents’ house in Covina, Calif., where he shot nine people to death and then burned the house. He later killed himself.
Sept. 2, 2008: Isaac Zamora, 28, was accused of killed six people in Alger, Wash., and wounding two others before turning himself into authorities. His mother described him to The Seattle Times as “extremely mentally ill,” and authorities said he had been released from jail the month before.
Feb. 14, 2008: A former graduate student at Northern Illinois University in DeKalb, Ill., opened fire in a lecture hall, killing five students and wounding several others before shooting himself.
Feb. 2, 2008: Six women were bound with duct tape during a robbery at a Lane Bryant store in Chicago. Five were shot to death; one was shot and survived. The shooter remains unknown.
Dec. 24, 2007 – Michele Anderson and her boyfriend, Joseph McEnroe, both 29, were accused of shooting six of the woman’s family members to death in Carnation, Wash.
April 16, 2007: Student Seung-Hui Cho, 23, killed 32 people at Virginia Tech before fatally shooting himself.
April 20, 1999: Eric Harris, 18, and Dylan Klebold, 17, killed 12 classmates and a teacher and wounded 26 at Columbine High School in Littleton, Colo. They then killed themselves.
Oct. 16, 1991: George Hennard crashed his pickup through the wall of a Luby’s Cafeteria in Killeen, Texas, then shot 23 people to death and wounded 20. He then killed himself.
June 18, 1990: James Edward Pough killed 10 and wounded four in a General Motors Acceptance Corp office in Jacksonville, Fla. He then killed himself.
Aug. 20, 1986: Postal worker Pat Sherrill, 44, shot 14 at a post office in Edmond, Okla., before killing himself.
July 18, 1984: James Oliver Huberty, 21, killed 21 at a San Ysidro, Calif., McDonald’s before being killed by a police sharpshooter.
July 12, 1976: California State University custodian Edward Charles Allaway killed seven co-workers and wounded two.
Aug. 1, 1966: Charles Whitman pointed a rifle from the observation deck of the University of Texas at Austin’s Tower and began shooting in a homicidal rampage that went on for 96 minutes. Sixteen people were killed and 31 were wounded.
Sept. 5, 1949: World War II veteran Howard Unruh, 28, shot and killed 13 neighbors in Camden, N.J. He was committed to a state mental institution.