With at least 50 people killed, the massacre early Sunday morning at an Orlando nightclub is the deadliest single-day mass shooting in the modern history of the United States — by nearly double the previous most deadly incident.
Here are America's deadliest mass shootings in modern times:
At least 50 people are killed and some 50 others are wounded after a gunman opened fire and took hostages at a gay nightclub in Orlando, Florida, early on the morning of Sunday June 12. Officials said a hostage situation developed after the gunman, identified as Omar Mateen, stormed the Pulse Nightclub about 2 a.m. Read more.
On April 16, 2007, 23-year-old Virginia Tech student Seung-Hui Cho shot 32 people to death on the Blacksburg, Virginia, campus before killing himself. The dead included 27 students and five faculty members. Another 17 people were injured. Days after the shooting, the worst school shooting in the nation's history, NBC News received a package from Cho that contained a video of him ranting about rich "brats" and complaining about being bullied.
On Dec. 14, 2012, 20-year-old Adam Lanza killed 28 people, including himself, his mother, 20 elementary school kids and six school staff and faculty at Sandy Hook Elementary School in Newtown, Connecticut. Lanza suffered from extreme mental health issues that weren't treated, and was preoccupied with violence, a report from state officials found. He also had easy access to weapons, the report said.
In Photos: Gunman Opens Fire at Orlando Nightclub
On Oct. 16, 1991, A 35-year-old named George Hennard crashed his pickup through Luby's Cafeteria, a packed restaurant in Killeen, Texas. He shot and killed 23 people before shooting and killing himself. Twenty-seven others were wounded. The Texas massacre is the deadliest shooting to not happen at a school in U.S. history. According to a former roommate, Hennard "hated blacks, Hispanics, gays. He said women were snakes."
On July 18, 1984, James Huberty, a 41-year-old former security guard who had lost his job, opened fire at a McDonald's in San Ysidro, California, killing 21 employees and customers, including children. A police sniper killed him an hour after he started shooting.
On Aug. 1, 1966, former U.S. Marine Charles Joseph Whitman, 25, killed his mother and wife, then went on top of a tower at University of Texas at Austin and killed 16 others. He also wounded at least 30. Whitman had complained of physical and mental health issues before the attack. He was then shot by a police officer. An autopsy after his death revealed he had a brain tumor, but it was not clear whether that had affected his actions.
On Dec. 2, 2015, 14 people were reported dead and an estimated 14 hurt in an attack at the Inland Regional Center in San Bernardino, California, a state-run facility that provides services to people with developmentally disabled people and trains social workers who care for them. The husband-and-wife assailants were eventually killed by police in a shootout.
On Aug. 20, 1986, postman Patrick Henry Sherill killed 14 postal workers in Edmond, Oklahoma, and then killed himself with a shot to the head. The rampage came a week after two supervisors reprimanded him for lousy performance.
On April 20, 1999, students Eric Harris, 18, and Dylan Klebold, 17, killed 12 other students and a teacher at Columbine High School in Littleton, Colorado. Two dozen were injured. They then killed themselves in the school's library. In journal entries, the high school seniors had written about a desire to imitate events such as the Oklahoma City bombing.
On Nov. 5, 2009, Mad. Nidal Malik Hasan, 39, killed 13 people and injured 32 others at Fort Hood, Texas. The massacre prompted the Army to come up with a list of 78 recommendations for Fort Hood to identify the potential for violent behavior among its soldiers. Hasan has been sentenced to death.
On April 3, 2009, in Binghamton, New York, 41-year-old Jiverly Wong, an immigrant, killed 13 people and injured four others at an immigrant services center before killing himself. President Obama called the shootings "an act of senseless violence."
On Feb. 18, 1983, three robbers at the Wah Mee gambling club in Seattle killed 13 people. Kwan Fai Mak and Benjamin Ng were convicted of murder later that year and are serving life sentences; Wai-Chu Ng was deported to Hong Kong last year.
On July 20, 2012, 24-year-old James Holmes sprayed bullets on a midnight screening of the new Batman movie at a theater in Aurora, Colorado. In addition to the 12 killed, 58 were wounded. Defense attorneys tried unsuccessfully to argue that he was insane at the time of the attack; he was sentenced to life in prison in August.
On Sept. 16, 2013, a 34-year-old named Aaron Alexis opened fire inside the Washington Navy Yard, killing 12. The former Navy reservist died in a gun battle with police.