Here’s what we know as of 1 p.m. ET:
Death toll: 50
This is the worst terror attack in the U.S. since 9/11 and the worst mass shooting in the history of the United States.
Patrons of the Pulse nightclub, which on its website describes itself as “the hottest gay bar in Orlando.” June is Pride Month.
The shooter has been identified as Omar Saddiqui Mateen, two law enforcement officials told CNN. The suspect is from Fort Pierce, Florida, officials say. Mateen is believed to be 29 years old.
He was shot and killed by Orlando police in an operation to free hostages he was said to be holding. It was suspected that he had a device strapped to his body, law enforcement sources said.
Neighbors and former classmates in Fort Pierce identified Mateen as the man in the attached photo.
Mateen was investigated by the FBI in the past for possibly having ties or being a sympathizer to Islamic extremism, according to a law enforcement official and a U.S. official. The law enforcement official told CNN that there were two cases opened on Mateen. The U.S. official said Mateen was not the main subject of at least one of those investigations. The investigations didn’t find evidence to charge him with anything.
In the past two weeks Mateen legally purchased a Glock pistol, found at the shooting scene, from a St. Lucie County area gun store, the law enforcement official said. He worked as a security guard, which allowed him to have a firearms license that meant minimal background checks when he bought guns.
The U.S. official said investigators have talked to Mateen’s family, who indicated he had expressed anti-gay feelings in the past.
The initial timeline
2 a.m. — Patron Christopher Hansen says he “just saw bodies going down.” The shooting “could have lasted a whole song,” he says.
To escape, customers had to jump an estimated six-foot privacy fence, since there was only one way out, a person who was at Pulse Nightclub during the shooting told CNN. The front door is the only way in and out of the nightclub, the witness said. The nightclub has two big rooms inside, one with a stage and a bar, and one room that is called the “White Room,” with its own bar and dance floor.
5 a.m. — An armored vehicle broke down the door and a wall for police to enter the club. It was during that assault that police said Mateen was shot dead by officers.
FBI teams, along with local law enforcement, are working to clear the apartment where the shooter lived in Fort Pierce, a federal law enforcement told CNN.
Agents are going through the apartment with bomb squads and investigating materials there, the source said.
“This is clearly an act of terrorism,” Florida Gov. Rick Scott said Sunday as he spoke to reporters about the shooting. “It’s sickening,” he said. “It should make every American angry.”
President Barack Obama was to address the nation at 1:30 p.m. Sunday in the wake of the mass shooting. He will be speaking in the White House briefing room.
There has been no claim of responsibility for the Orlando nightclub terror attack on jihadi forums, but ISIS sympathizers reacted by praising the attack on pro-Islamic State forums, according to CNN Terrorism Analyst Paul Cruickshank.