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. Here’s what we know about the deadliest mass shooting in U.S. history:

WHAT HAPPENED:

Police say Omar Mateen, equipped with an assault rifle and a handgun, opened fire on patrons early Sunday. He also exchanged fire with an officer working at the club about 2 a.m., when more than 300 people were inside.

Police say the gunman then went back inside and took hostages. Police sent in a SWAT team to rescue hostages about 5 a.m. and Mateen died in an exchange of gunfire with SWAT officers.

THE SHOOTER:

Authorities have identified the shooter as 29-year-old Omar Mateen of Fort Pierce, Florida.

In a 911 call from the club, Mateen professed allegiance to the leader of the Islamic State, Abu Bakr al-Baghdadi.

Mateen was a U.S. citizen born in New York. His ex-wife said his family was from Afghanistan.

Authorities say Mateen was not under surveillance, but that in 2014, they discovered he had ties to an American suicide bomber. They said the ties were minimal and they didn’t think he represented a threat at the time.

They say he also made inflammatory comments to co-workers in 2013.

Authorities also say Mateen legally purchased at least two firearms within the past week or so.

Security company G4S said in a statement to the Palm Beach Post that he had been an employee of the company since September 10, 2007.

Mateen’s father, Seddique Mir Mateen, 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. The father said the attack had nothing to do with religion.

MASS CASUALTIES:

At least 50 people were killed, 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 VICTIMS:

The city of Orlando is publishing the names of those killed on its website after their families have been contacted. The list can be found here

THE REACTION:

President Barack Obama says the nightclub shooting in Orlando was an “act of terror” and an “act of hate.” Speaking from the White House, Obama says the United States has to decide if that is the “country we want to be.” He says that doing nothing is a decision as well.

Prime Minsiter Justin Trudeau offered Canada’s condolences to the victims. “We gr2ieve with our friends in the US & stand in solidarity with the LGBTQ2 community after today’s terror attack”

Ontario Premier Kathleen Wynne, who is openly gay, wrote on Twitter: “Shocked and heartbroken by the news of the #Orlando terrorist attack. Our thoughts are with the entire #LGBTQ2S community.”

From the U.S. Ambassador to Canada, Bruce A Heyman: “Thank you to all our Canadian friends for the outpouring of support today. Your extraordinary friendship is valued and appreciated.”

American Muslim leaders are condemning the attack. Nihad Awad, the executive director of the Council on American-Islamic Relations, called the killings a hate crime and said the group has no tolerance for extremism of any kind. Awad says members of the LGBT community have stood with Muslims in the past and today they stand that community.

About 100 people, many draped in rainbow flags, gathered in Paris for a spontaneous vigil at Place Igor Stravinsky to remember those slain and wounded. They lit candles and took pictures as a person in head-to-toe fetish gear held up a sign saying “Proud.” One woman carried a poster showing a ribbon with a rainbow on one side and an American flag on the other. “To Orlando, we have love,” it read.

Prime Minister Benjamin Netanyahu says Israel stands “shoulder to shoulder” with the United States after the shooting. Netanyahu said Sunday that “on behalf of the people and government of Israel, I extend our deepest condolences to the American people following last night’s horrific attack on the LGBT community in Orlando.”

At the Tony Awards celebration, organizers dedicated Sunday’s ceremony to the victims. Host James Corden opened Broadway’s biggest night with a message for the fallen in Orlando: “Our hearts go out to all of those affected by this atrocity. All we can say is you’re not on your own right now. You’re tragedy is our tragedy,” he said in part, adding:”Hate will never win. Together we have to make sure of that. Tonight’s show stands as a symbol and a celebration of that principle. This is the Tony Awards.”

SECOND DEADLY SHOOTING IN TWO DAYS:

The attack follows the fatal shooting late Friday of 22-year-old singer Christina Grimmie, who was killed after her concert in Orlando by a 27-year-old Florida man who later killed himself. Grimmie was a YouTube sensation and former contestant on “The Voice.”

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