What to Know About the Pulse Nightclub Shooting in Orlando
A gunman opened fire in an Orlando nightclub early Sunday morning, killing 50 people and wounding another 53 in the worst mass shooting in U.S. history. The FBI says the attack is being investigated as an act of terrorism. Here's what we know so far, What happened, A shooter armed with an assault-type rifle and a handgun opened fire at the crowded Pulse Orlando, a gay nightclub, at about 2 a.m. police said. At one point he left the club and exchanged shots with an officer outside, then he went back in and took hostages, the Associated Press reports. A SWAT team went into the club at about 5 a.m. to rescue the hostages, and the shooter was killed in the ensuing gun battle, the AP reports. The gunman , The shooter has been identified as Omar Mateen, 29, of Port St. Lucie, Florida. authorities said. Mateen had reportedly made calls to 911 early Sunday stating his allegiance to ISIS. He was first flagged on the FBI's radar in 2013 and then again in 2014, FBI Assistant Special Agent in Charge Ron Hopper said at a news conference. Both investigations were closed after inconclusive interviews. The agency interviewed Mateen twice after being alerted to him speaking of possible terrorist ties in 2013 but officials were "unable to verify the substance of his comments." Mateen came to the FBI's attention again in the next year over possible ties to an American suicide bomber, Hopper said. The FBI closed that investigation after authorities determined that contact between the two were minimal. Mateen did not pose as a threat at that time, Hopper said. Mateen is a U.S. citizen who was born in New York and later moved to Florida, authorities said. He was not under investigation or surveillance at the time of the Orlando nightclub massacre, according to the FBI. Mateen had legally purchased at least two firearms  a handgun and a long gun  within the last week, the ATF said. A security company, G4S, said Sunday that Mateen had been employed there since 2007, adding that it was "shocked and saddened" by the shooting. "We are cooperating fully with all law enforcement authorities," the company said. The victims, Orlando officials released the names of the first four victims late Sunday afternoon. Among those killed were Edward Sotomayor Jr. Stanley Almodovar III, Luis Omar Ocasio-Capo and Juan Ramon Guerrero, according to an official web page the city designed to post updates on the deceased. Authorities said 50 people were killed and another 53 were hospitalized. Dr. Michael Cheatham of the Orlando Regional Medical Center said many of the shooting victims are in critical condition. He said those looking to donate blood can visit local blood banks. "That would be a tremendous help," he said. The nightclub, The shooting occurred at Pulse Orlando, which the Times described as one of the biggest gay nightclubs in the Florida city. As the shooting unfolded, the club posted on Facebook, "everyone get out of pulse and keep running." A couple hours later, the club wrote on Facebook "As soon as we have any information we will update everyone. Please keep everyone in your prayers as we work through this tragic event. Thank you for your thoughts and love.", The investigation , Authorities descended on the nightclub Sunday to investigate the shooting, and were working to determine a motive, whether the gunman acted as a lone wolf and whether there was any connection to international terrorism. It was not immediately clear why the gunman targeted Pulse Orlando. ISIS has claimed responsibility for the shooting, saying the attack was "carried out by an Islamic State fighter" in a report on its official Amaq news agency. President Obama was briefed on the attack Sunday morning and will receive updates as the FBI and other federal and local authorities investigate. Florida Governor Rick Scott declared a state of emergency, as did the city of Orlando. "This is clearly an act of terror," Scott told reporters at a news conference.