ORLANDO, Florida (CNN) — An American-born man who’d pledged allegiance to ISIS gunned down 50 people early Sunday at a gay nightclub in Orlando — the deadliest mass shooting in the United States and the nation’s worst terror attack since 911, authorities said.
* The gunman, Omar Mateen, 29, of Fort Pierce, Florida, was interviewed by the FBI in 2013 and 2014 but was not found to be a threat, the FBI said.
* Mateen called 911 shortly before the attack to pledge allegiance to ISIS and mentioned the Boston Marathon bombers, according to a U.S. official.
* Orlando police shot and killed Mateen.
Mateen carried an assault rifle and a pistol into the packed Pulse club about 2 a.m. Friday and started shooting, killing 50 people and wounding at least 53, police said.
After a standoff of about three hours — while people trapped inside the club desperately called and messaged friends and relatives — police crashed into the building with an armored vehicle and killed Mateen.
“It appears he was organized and well-prepared,” Orlando Police Chief John Mina said early Sunday. Authorities say they haven’t found any accomplices.
‘An act of hate’
There has been no claim of responsibility for the attack on jihadi forums, but ISIS sympathizers have reacted by praising the attack on pro-Islamic State forums.
“We know enough to say this was an act of terror and act of hate,” President Obama said in an address to the nation from the White House.
While the violence could have hit any American community, “this is an especially heartbreaking day for our friends who are lesbian, gay, bisexual or transgender,” he said.
Omar Mir Seddique Mateen was born in 1986 in New York City. Most recently he lived in Fort Pierce, about 120 miles southeast of Orlando. He had worked since 2007 as a security officer at G4S Secure Solutions, one of the world’s largest private security companies.
Mateen’s parents, who are from Afghanistan, said he’d expressed outrage after seeing two men kiss in Miami, but didn’t consider him particularly religious.
Mateen was interviewed by the FBI in 2013 and 2014 after he expressed sympathy for a suicide bomber, FBI Assistant Special Agent Ronald Hopper told reporters Sunday.
“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.
In the past two weeks Mateen legally purchased a Glock pistol and a long gun, 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.
‘Closer and louder and louder’
Pulse describes itself as “the hottest gay bar” in the heart of Orlando. Hours before the shooting, the club urged partygoers to attend its “Latin flavor” event Saturday night. The club is a vast, open space that was hosting more than 300 patrons late Saturday and into Sunday morning.
People inside the cavernous nightclub described a scene of panic made more confusing by the loud music and darkness.
Christopher Hansen said he was getting a drink at the bar about 2 a.m. when he “just saw bodies going down.” He heard gunshots, “just one after another after another.”
The gunshots went on for so long that the shooting “could have lasted a whole song,” he said.
When the shots erupted, Hansen hit the ground, crawling on his elbows and knees, before he spotted a man who had been shot.
“I took my bandana off and shoved it in the hole in his back,” Hansen said, adding that he saw another woman who appeared to be shot in the arm.
Luis Burbano was with his best friend inside the club when they realized the pop, pop, pop they were hearing wasn’t the music but gunfire.
It was getting, “closer and louder and louder,” he told CNN’s Jake Tapper. He and his friend noticed a 10-second break in the shooting, so they managed to make a break for the door.
“We tried to save ourselves and as many people as we could to make it out of there,” he said.
Once outside he saw a young man collapse in front of him. “I grabbed him not realizing that his forearm was split in two,” Burbano said.
He acted fast by ripping off his shirt and tightening it around the man’s arm to try to slow the bleeding.
Ricardo Negron Almodovar escaped the club and posted this description on his Facebook page: “People on the dance floor and bar got down on the floor and some of us who were near the bar and back exit managed to go out through the outdoor area and just ran.”
Video from CNN affiliate WKMG captured clubgoers carrying injured people from the club.
After the initial shooting, police surrounded the club while Mateen was inside with clubgoers hiding in bathrooms and other parts of the building. People inside the club were communicating on their phones with law enforcement from that time until around 5 a.m., when authorities used an armored vehicle to break down the door of the building.
Hospital swamped with victims
Thirty-nine people and Mateen were pronounced dead at the scene, with two bodies found in the parking lot, Mayor Buddy Dyer said. Eleven people were taken to hospitals and pronounced dead there, he said.
Forty-three of the wounded people were patients on Sunday afternoon at Orlando Regional Medical Center, a hospital spokesperson said, with 26 operations being performed.
Before Sunday, the deadliest shootings in U.S. history were at Virginia Tech in 2007 and Sandy Hook Elementary School in 2012, with 32 and 27 killed.
National media attention was already focused on Orlando over the weekend because of Friday night’s fatal shooting of Christina Grimmie, an up-and-coming singer who had appeared on NBC’s “The Voice,” while she signed autographs after a show. Her shooter then killed himself. The Pulse shooting occurred only a few miles from the Plaza Live theater, where Grimmie was killed.
“We need to support each other. We need to love each other. And we will not be defined by a hateful shooter,” said Dyer, the mayor.
President Obama called for flags to be lowered to half staff and Florida Gov. Rick Scott called for a moment of silence across the nation at 6 p.m. Sunday. States of emergency were declared for the city of Orlando and for Orange County.
Also on Sunday, authorities in West Hollywood, California, took a suspect into custody after discovering an arsenal in his car that included explosive powder, assault weapons and a camouflage outfit, CNN affiliate KABC reported, citing unnamed authorities. The suspect told authorities he was there for the Los Angeles Pride festival, which is underway this weekend.
There was no indication that the arrest was related to the Orlando attack.
Eleven Orlando police officers and three sheriff’s deputies who exchanged gunfire with the suspect will be temporarily relieved of duty pending an investigation.
One officer suffered an eye injury when a bullet struck his Kevlar helmet, said Danny Banks, special agent in charge of the Florida Department of Law Enforcement’s Orlando bureau. The helmet saved the officer’s life, Banks said.
CNN’s terrorism analyst Paul Cruickshank, John Couwels, Joe Sutton, Vivian Kuo, Deborah Bloom, Pamela Brown, Evan Perez, Shimon Prokupecz, and MaryLynn Ryan contributed to this report