ORLANDO — (CNN) Here’s what we know about the Orlando, Florida, terror attack as of 5:04 a.m. ET Monday

Casualties

Death toll: 50

Hospitalized: 53

This is the worst terror attack in the United States since 9/11 and the worst mass shooting in the history of the United States.
The target

Patrons of the Pulse nightclub, which on its website describes itself as “the hottest gay bar in Orlando,” were targeted. June is Pride Month. Between 300 and 350 people were at the club.

The attack occurred in two areas of the nightclub.

Owner of Pulse: Barbara Poma released the following statement: “Like everyone in the country, I am devastated about the horrific events that have taken place today. Pulse, and the men and women who work there, have been my family for nearly 15 years.

“From the beginning, Pulse has served as a place of love and acceptance for the LGBTQ community. I want to express my profound sadness and condolences to all who have lost loved ones. Please know that my grief and heart are with you.”

The survivors

Dramatic details about how some employees and patrons of the Pulse nightclub survived have been told by a source close to the nightclub’s owners and employees:

-One person hid in the bathroom covered herself with dead bodies to protect herself. She survived.

-Some entertainers hid in the dressing room when the shooting started. They were able to escape the building when police removed the air conditioning unit and crawled out.

-One of the bartenders said that she was hiding under the glass bar. Police came in and said, “If you are alive, raise your hand.” Then police got them out.

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The shooter

Identified as Omar Mir Seddique Mateen, 29, of Fort Pierce, Florida.

U.S. citizen, born Nov. 16, 1986 in New York. Parents are originally from Afghanistan.

Shot dead by Orlando police in an operation to free hostages the shooter had taken.

The family of the shooter: They told investigators Mateen wasn’t particularly religious from what they observed. They expressed surprise about any connection to ISIS, according to two law enforcement officials.

Mateen did express outrage to his father after seeing two men kissing in Miami, investigators say.

Shooter’s ex-wife: Sitora Yusufiy said her ex-husband had issues with anger. Mateen was a normal husband at the beginning of their marriage but a few months in, he started abusing her. Mateen was “bipolar” she said, but he was not formally diagnosed.

Investigation

Authorities are looking into possible self-radicalization, into the shooter’s electronic devices for any suspicious activity and trying to put together a timeline of his movement.

FBI investigation: Shooter was interviewed by the FBI in 2013 and 2014, FBI Assistant Special Agent in Charge Ronald Hopper told reporters Sunday. He was the subject of the 2013 investigation and was interviewed in the 2014 one. “Those interviews turned out to be inconclusive, so there was nothing to keep the investigation going,” Hopper said. Mateen was not under investigation at the time of Sunday’s shooting and was not under surveillance, Hopper said.

Suspected ISIS sympathizer: Law enforcement officials say Mateen was known to the FBI, one of hundreds of people suspected of being ISIS sympathizers who are on the FBI’s radar according to two law enforcement officials. There was no indication he was plotting to carry out an attack the officials said. The investigators haven’t found evidence yet to show that he did this on behalf of ISIS.

But the earlier knowledge about his possible sympathies explains why they are treating this as likely Islamic terror-related.

The guns: Shooter purchased a handgun and a long gun within the last few days, ATF Assistant Special Agent in Charge Trevor Velinor told reporters. “He is not a prohibited person. They can legally walk into a gun dealership and acquire and purchase firearms. He did so. And he did so within the last week or so,” Velinor said.

More guns found: Investigators recovered a .38-caliber Smith and Wesson revolver from the shooter’s vehicle, according to a law enforcement official. ATF is working to trace it.

The vehicle: A law enforcement source tells CNN Mateen rented a vehicle and drove to Orlando to carry out the attack. That vehicle was right outside Pulse, according to Orlando’s police chief.

Past employment: He worked as a security guard — that allowed him to have a firearms license, and minimal background checks when he bought firearms. According to a neighbor who saw him regularly, Mateen worked as a security guard at the Port St. Lucie courthouse. The neighbor said Mateen often worked security in the front of the building, manning the metal detectors.

Reaction

President Barack Obama: Called the Orlando attack an “act of terror and an act of hate.” He ordered flags to be flown at half-staff. This is the 15th time Obama has made an address in response to a mass shooting.

Obama’s first campaign appearance with presumptive Democratic presidential candidate Hillary Clinton has been postponed because of the Orlando shootings, the campaign announced.

Florida Gov. Rick Scott: “This is clearly an act of terrorism. It’s sickening,” he said. “It should make every American angry.”

Pope Francis: “We all hope that ways may be found, as soon as possible, to effectively identify and contrast the causes of such terrible and absurd violence.”

No claim of responsibility: 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.

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