A gunman opened fire at a gay night club in Orlando, Florida, early Sunday, killing 50 people and wounding 53 more before he was killed in a shootout with SWAT team members. Authorities say he may have had a connection with radical Islamic terrorism, and his father said he became angry a couple of months ago when he saw two gay men kissing. Here’s what we know about the deadliest mass shooting in U.S. history:

___

MASS CASUALTIES: At least 50 people are dead, and 53 were hospitalized, most in critical condition, officials said. A surgeon at Orlando Regional Medical Center said the death toll was likely to climb.

___

THE SHOOTER: Authorities have identified the shooter as 29-year-old Omar Mateen of Port St. Lucie, Florida. In a 911 call from the club, Mateen professed allegiance to the leader of the Islamic State, Abu Bakr al-Baghdadi, according to a law enforcement official familiar with the investigation who was not authorized to discuss the matter publicly and spoke on condition of anonymity.

The FBI says Mateen was a U.S. citizen and not under surveillance. In 2014, authorities discovered he had ties to an American suicide bomber, but they said they were minimal, and he didn’t constitute a threat at the time. They say he also made inflammatory comments to co-workers in 2013. Mateen legally purchased at least two firearms within the past week or so, said Trevor Velinor, an agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Mateen’s father, Mir Seddique, said his son got angry when he saw two men kissing in Miami a couple of months ago. He said that might be related to the attack. Seddique said the attack had nothing to do with religion. Mateen’s ex-wife said his family was from Afghanistan, but that he was born in New York.