49 Killed in Orlando Gay Nightclub Shooting; Largest Mass Shooting in U.S. History

Orlando Shooting - H getty 2016
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President Obama calls the massacre "an act of terror and an act of hate" as federal law enforcement and national security investigate. The shooting might also have inspired a copycat plan as a man was arrested allegedly planning a similar assault on Los Angeles' gay pride festivities.

A gunman killed 49 people and left 53 injured early Sunday morning in a crowded Orlando, Fla., gay nightclub in what marks the worst mass shooting in American history, and law enforcement officials are calling it an act of terrorism.

The shooter, whom federal law enforcement officials identified as Omar Mir Seddique Mateen, stormed the Pulse nightclub wielding an assault-type rifle and a handgun. The 29-year-old opened fire on the crowd before dying in a gunfight with SWAT officers, police said Sunday.

Initial reports said 50 people were killed, and that was revised to 49, with Mateen being the 50th death.

Mateen allegedly called 911 himself and pledged allegiance to ISIS, claiming credit for the massacre, according to reports. And the shooting might have already inspired a copycat attack: Santa Monica police arrested a man armed with explosives, assault rifles and ammunition who told police he was headed to the West Hollywood gay pride parade.

President Barack Obama addressed the nation regarding the tragedy, saying the White House is working with the FBI and national security to investigate the shooting and that more will be known in the coming days. He called the shooting "the most deadly shooting in American history" and ordered American flags to be flown at half-staff across the nation.

"We know enough to say this is an act of terror and an act of hate," President Obama said in the five-minute speech before reporters. "We are united in grief and resolve to defend our people."

Obama said the shooting is a further reminder of how easy it is for someone to get a weapon that allows them to shoot people in a school, in a house of worship, a movie theater or a gay nightclub.

Speaking from the White House, Obama said the United States has to decide if that is the "country we want to be." He said that doing nothing is a decision as well.

Vice President Joe Biden echoed the president's comments in a statement saying, "Jill and I offer our prayers and deepest condolences for all those affected by today’s horrific events. But our prayers are not enough to end these kinds of senseless mass shootings. The violence is not normal, and the targeting of our lesbian, gay, bisexual and transgender Americans is evil and abhorrent. … Times of unspeakable tragedy and evil like this are the moments to remind the killers, and the world, of what is best in us, and what unites us."

The incidents occurred during LGBT Pride Month, which also is going strong with festivities in Los Angeles this weekend. Law enforcement and government officials in Los Angeles say they are coordinating with federal authorities to beef up security during the West Hollywood parade. Similar statements have been pledge by other cities holding festivities.

In Orlando, Police Chief John Mina said police are still investigating the massacre that left the Pulse nightclub's parking lot looking like a triage scene. The shooting occurred around 2 a.m., when the club had some 300 people inside, many of whom fled as gunshots rang out.

However, Mateen was still able to hold a number of the patrons hostage. Orlando SWAT teams launched a rescue mission at around 5 a.m., in which the shooter was killed. Pulse posted on its Facebook page around 2 a.m.: "Everyone get out of pulse and keep running." Just before 6 a.m., the club posted an update: "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."

A surgeon at Orlando Regional Medical Center said the death toll was likely to climb.

"There's blood everywhere," Orlando Mayor Buddy Dyer said.

Meanwhile, the city of Orlando's website has begun releasing the names of the victims.

Witnesses described a chaotic scene when the gunfire began shortly before the club known as Pulse was to close.

"Some guy walked in and started shooting everybody. He had an automatic rifle, so nobody stood a chance," said Jackie Smith, who had two friends next to her get shot. "I just tried to get out of there."

Mateen's father, Seddique Mir Mateen, told NBC News that his son was enraged after seeing two men kissing in Miami months ago. "This has nothing to do with religion," said Seddique. "We are saying we are apologizing for the whole incident. We weren't aware of any action he is taking. We are in shock like the whole country.

"I apologize for what my son did," Seddique said to NBC News. "I don't know why he did it. He is dead, so I can't ask him. I wish I knew."

Mateen was an American citizen from Port St. Lucie, Fla., who had worked as a security guard. Mateen's ex-wife said his family was from Afghanistan but that her ex-husband was born in New York. His family later moved to Florida.

The shooter in 2013 made inflammatory comments to co-workers, and Mateen was interviewed twice, FBI agent Ron Hopper said. He called those interviews inconclusive.

In 2014, Hopper said, officials found that Mateen had ties to an American suicide bomber. He described the contact as minimal, saying it did not constitute a threat at the time.

Mateen purchased at least two firearms legally within the last week or so, according to Trevor Velinor of the Bureau of Alcohol, Tobacco and Firearms.

Hopper said during a press conference that there was no further threat to Orlando or the surrounding area. When asked if the gunman had a connection to radical Islamic terrorism, Hopper said authorities "have suggestions that individual has leanings towards that."

Mina Justice was outside the club early Sunday trying to contact her 30-year-old son, Eddie, who texted her when the shooting happened and asked her to call police. He told her he ran into a bathroom with other club patrons to hide. He then texted her: "He's coming."

"The next text said: 'He has us, and he's in here with us,'" she said. "That was the last conversation."

Jon Alamo said he was at the back of one of the club's rooms when a man holding a weapon came into the front of the room.

"I heard 20, 40, 50 shots," Alamo said. "The music stopped."

Clubgoer Rob Rick said the shooting started just before closing time: "Everybody was drinking their last sip," he said.

The Human Rights Campaign on Sunday morning released a statement on the shooting, saying HRC has lowered its flag to half-mast.

"We are devastated by this tragic act of violence, which has reportedly claimed the lives of at least 50 LGBTQ people and allies and injured more than 50 others,” said HRC president Chad Griffin. “We are grieving for the victims and our hearts are broken for their friends, families, and for the entire community. This tragedy has occurred as our community celebrates pride, and now more than ever we must come together as a nation to affirm that love conquers hate.”

Read the full statement here

The attack follows the fatal shooting late Friday of 22-year-old singer Christina Grimmie, who was murdered 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.

The Associated Press contributed to this story.