The sound of gunfire on school grounds large and small has haunted the U.S. for years. From the horrors of Columbine to the heartbreak of Sandy Hook, school shootings have become a fact of life for many.
On Monday, two people were reported killed in a possible murder-suicide at an elementary school in San Bernardino, Calif. "We believe this to be a murder suicide," Police Chief Jarrod Burguan tweeted. "Happened in a class room. Two students have been transported to the hospital."
Burguan later said that two adults were deceased and two people, possibly students, were wounded and taken to a hospital.
Among school shootings in the past two decades:
• April 20, 1999: Students Eric Harris, 18, and Dylan Klebold, 17, open fire at Columbine High School in Littleton, Colo. They kill 12 students and one teacher and wounded more than 20 others before killing themselves in the school's library.
• Feb. 29, 2000: A 6-year-old boy shoots and kills classmate Kayla Rolland, also 6, at Theo J. Buell Elementary School in Mount Morris Township, Mich. The boy is not charged because of his age.
• May 26, 2000: Honor student Nathaniel Brazill, 13, shoots and kills his teacher Barry Grunow on the last day of classes at Lake Worth Community Middle School in Lake Worth, Fla. He is sentenced to 28 years in prison.
• March 5, 2001: Charles "Andy" Williams, 15, opens fire inside a Santee, Calif., high school, killing two students and injuring 13 others. He is later sentenced to 50 years to life in prison.
• Sept. 24, 2003: John Jason McLaughlin, a 15-year-old freshman at Rocori High School in Cold Spring, Minn., shoots and kills classmates Aaron Rollins, 17, and Seth Bartell, 15. McLaughlin is convicted of murder and sentenced to life in prison.
• March 21, 2005: Jeff Weise, 16, kills his grandfather and a companion of his grandfather's, then heads to a high school on the Red Lake Indian Reservation in Minnesota. He kills five students, a teacher and a security guard before taking his own life.
• Sept. 29, 2006: Eric Hainstock, 15, shoots and kills John Klang, 49, principal of Weston High School in Cazenovia, Wis. Klang had issued Hainstock a warning the day before for having tobacco at school. Hainstock was sentenced to life in prison.
• Oct. 2, 2006: Milk-truck driver Charles C. Roberts, 32, enters a one-room Amish schoolhouse in Nickel Mines, Pa. He isolates the female students in the classroom before methodically executing them. He kills five girls and wounds several more. Roberts then commits suicide.
• April 16, 2007: Gunman Seung-Hui Cho, 23, kills two people in a dormitory at Virginia Tech. A few hours later, Cho enters an academic building on the Blacksburg campus and kills 30 more people and himself.
• Feb. 14, 2008: Steven Kazmierczak, 27, enters a lecture hall at Northern Ilinois University campus in DeKalb and kills five students and wounds 18 others before taking his own life.
• Dec. 14, 2012: Adam Lanza, 20, guns down 20 children and six adults at Sandy Hook Elementary School before killing himself.
• Feb. 27, 2012: Three students are killed when T.J. Lane, 17, opens fire inside the cafeteria of the Chardon High School in Ohio. Lane is sentenced to life in prison.
• June 7, 2013: John Zawahri, 23, kills his father and brother and sets their home on fire before going to Santa Monica College. There, he randomly shoots at cars, killing three more and wounding others before he is killed by police.
• Aug. 27, 2015: A Savannah State University student who was a former football standout was fatally shot during an altercation in the Georgia school’s student union.
• Oct. 1, 2015: Student Christopher Harper-Mercer, 26, opened fire in a hall on the Umpqua Community College Campus in Roseburg, Ore., killing eight students and one teacher and injuring nine others. Mercer later committed suicide.
• Feb. 12, 2016: Two 15-year-old girls died in an apparent murder-suicide at Independence High School in Glendale, Ariz.