Prior to Monday's massacre at a country music concert in Las Vegas, the June 2016 shooting inside an Orlando gay nightclub was the deadliest mass shooting in U.S. history.
The following is a partial list of some of the worst mass shootings in the United States since 1999.
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June 12, 2016: At least 50 people were killed and 53 wounded, many of them critically, in a shooting in a gay nightclub in Orlando, Florida.
December 2, 2015: 14 killed in San Bernardino, California, during a party inside a local government center; suspects Syed Farook and Tashfeen Malik are killed following a car chase and shootout with police.
June 18, 2015: Nine people are shot dead in a historic black church in Charleston, South Carolina. Dylann Roof, 21, is indicted.
December 14, 2012: A massacre at Sandy Hook Elementary School in Newtown, Connecticut, leaves 20 children and six teachers dead. Gunman Adam Lanza kills himself.
July 20, 2012: A mass shooting at a movie theatre in Aurora, Colorado, during a midnight screening of the film "The Dark Knight Rises," leaves 12 dead and 70 wounded. James Eagan Holmes is handed down 12 life sentences without parole and an additional 3,318 years in prison.
April 16, 2007: Student Seung-Hui Cho shoots and kills 32 people on the campus of the Virgina Polytechnic Institute in Blacksburg, Virgina, before committing suicide.
April 20, 1999: Teenagers Eric Harris and Dylan Klebold shoot and kill 12 pupils and a teacher at Columbine High School in Littleton, Colorado. At least 21 people are injured. The pair committed suicide.