A reggaeton song was pounding in the club's speakers as Jeannette McCoy, 37, danced close to her friend Angel in the wee hours of Sunday morning.
Dozens of sweaty people packed the floor at the Orlando gay nightclub Pulse. Club lights threw patches of purple across the dance floor. As one song ended, McCoy waited for the DJ to play another, but instead she heard a very different sound.
"It was just pop-pop-pop-pop-pop-pop-pop," she said. "The shots were continuous."
A heavily armed man who earlier had sworn allegiance to the terrorist group ISIS opened fire inside the crowded club, killing at least 50 people and wounding 53 in the country's worst mass shooting. Several hours later, he was fatally shot after exchanging gunfire with police.
Inside Pulse, the evening had been winding down when bullets sprayed the air. Chaos and confusion followed. Some clubgoers initially assumed the gunshots were part of the thumping soundtrack to the club's "Upscale Latin Saturdays" party.
But as the reality of the situation became clear, hundreds of people rushed for the exits, tumbling into the dark night, some of them bleeding and screaming. Others fell to the ground, where some pretended to be dead.
The club's staff issued a grim warning on its Facebook page: "Everyone get out of pulse and keep running."
Hours later, after the death toll had secured the day's place as among the bloodiest in recent American history, the Islamic State released a statement claiming responsibility for the attack and calling the gunman an "Islamic State fighter."
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Federal law enforcement officials identified the shooter as Omar Mir Seddique Mateen, 29, an American citizen of Afghan descent who was born in New York and lived in Fort Pierce. Shortly before he entered the club, he called 911 and pledged his support for the Islamic State, a sympathy also cited by the husband and wife who killed 14 people in San Bernardino, Calif., in December.
At a news conference Sunday, federal officials said the FBI became aware of Mateen in 2013 after co-workers reported him for making comments that suggested he had ties to terrorist groups. At another point, he was thought to have connections to suicide bomber Moner Mohammad Abusalha, an American who grew up in Florida and died in Syria in 2014.
The FBI interviewed Mateen at least three times in recent years, but was unable to find any incriminating evidence, said Ronald Hopper, an assistant agent in charge of the bureau's Tampa Division. The agency ultimately closed its investigations.
FBI officials suggested Mateen acted alone and said they were not searching for a second gunman.
In an interview with NBC News, Mateen's father said his son was likely motivated not by religious extremism, but by his hatred of gay people.
Describing an incident in downtown Miami several months ago, Seddique Mir Mateen said his son "saw two men kissing each other in front of his wife and kid and he got very angry."
"We are not aware of any action he was taking," the father said. "We are in shock like the rest of America."
Since 2007, Mateen had worked as a licensed security officer for G4S, one of Florida's largest private security companies. Officials with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives said he legally bought two firearms in the past week — a long gun and a handgun — but declined to say where.
In a statement from the White House, President Barack Obama called the mass shooting "a further reminder of how easy it is for someone to get their hands on a weapon that lets them shoot people in a school, or in a house of worship, or a movie theater, or in a nightclub."
"We have to decide if that's the kind of country we want to be. And to actively do nothing is a decision as well," the president said.
The death toll from the Pulse massacre far exceeds that of the 2007 rampage at Virginia Tech, where 32 people were killed, making it the nation's worst mass shooting and the deadliest terrorist attack on American soil since Sept. 11, 2001.
Rasha Mubarak, the Orlando regional coordinator for the Council on American-Islamic Relations, released a statement condemning the attack.
"The Muslim community joins our fellow Americans in repudiating anyone or any group that would claim to justify or excuse such an appalling act of violence," she said.
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Armed with a .223-caliber AR-15-style semiautomatic style rifle and a 9mm handgun, Mateen walked into Pulse and opened fire at around 2 a.m. Although it was nearly last call, law enforcement officials said more than 300 people were inside, dancing and drinking, enjoying a place that many have described as a refuge for Orlando's gay community.
When the gunman opened fire, clubgoers shrieked and fell amid the darkness. They ran for the doors, stumbling over each other, as the air filled with smoke and flashes of gunfire.
As McCoy ran, she felt the heat of bullets whizzing past and bits of debris — shards of glass, wood, plastic — hitting her skin.
The shooter was not targeting anyone specific, she said, adding, "He tried to kill every single one of us in there."
Running to the right, through a large dance room and to the club's patio, she found the fence had already been knocked down, allowing her to escape. McCoy spotted a bartender bleeding from a wound in his right thigh on the pavement. She ripped off her blue-and-white crop top and wrapped it around his leg, she said.
"I had blood on my upper arms, a little bit on my face," McCoy said. "I had people's blood. It just wasn't my blood."
Inside the club, McCoy's friend, Yvens Carrenard, 29, was huddled under a computer desk in a crawl space above a storage room.
When he heard gunshots, Carrenard said he turned and ran into the room behind him. Five or six people followed, cramming into a space about the size of a walk-in closet.
The group climbed a ladder that led to an even smaller attic area, where they huddled until officers arrived and ushered them out through a side door. As he exited what had been a dance floor and was now the scene of a massacre, Carrenard stepped around bodies and streaks of blood.
"I looked down because I wanted to make sure that none of my friends were dead," he said.
Several dozen people who were unable to flee were held hostage inside the club until about 5 a.m., when tactical teams raided the building. Officials said 11 law enforcement officers exchanged fire with the gunman, who was killed at the scene. One officer was shot during the assault and saved by a Kevlar helmet, and at least 30 people were rescued, according to Orlando police Chief John W. Mina.
Investigators called to the scene told CNN that, hours later, the bodies remained where they had fallen, their cell phones ringing and vibrating, filling the club with the eerie sound of parents trying to reach children who would never pick up.
Around the country, as cities prepared to host celebrations of LGBT pride month, security was increased in response to the Pulse massacre. In Florida, financial support for victims poured in. Equality Florida said on Sunday that it had raised more than $1 million by 10 p.m.
Orlando police asked mourners to assemble at a green space downtown, rather than hold vigils around the city. Officers would have to staff each of the vigils, the department explained, creating "a serious strain on our limited resources, which we need to dedicate to law enforcement and victims."
In Orlando, the LGBT Center of Central Florida became a hub for mourners as the city's gay community rallied to provide support for survivors.
One man crouched against the wall, red-eyed, knees to his chest. As he clutched his phone, he said he was waiting for news. "My boyfriend," he said.
Center board member Rob Domenico said mothers had been calling frantically all morning, asking for updates on their sons.
"I've fielded so many phone calls today from mothers: 'Help me. Where's my son? I don't know where he is, I haven't heard from him,' " he said. "It's tearing us apart."
Obeying public health officials' desperate calls for donations, hundreds of people traveled to blood blanks around the region, some which ran out of supplies and were forced to close.
Alex Barrio of Orlando said he felt compelled to donate, as many gay men are not allowed to contribute. Under its revised policy, the U.S. Food and Drug Administration recommends refusing blood donations from men who have had sex with other men in the past 12 months.
"The people most affected can't donate," Barrio said. "It's something that should be changed."
Barrio, who is straight, said he used to live near Pulse and would go often.
"It's always been a place where anybody can go and have a good time," he said.
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Friends and family members of victims gathered outside of the nightclub Sunday, waiting for answers and to hear from loved ones they hoped were still alive. Among them was 28-year-old Stephen Walls, who held an American flag in his hand and said one of his friends had died in the shooting. Another seven of his friends were still missing.
"When you are at war, you expect this to happen," he said, recalling the year he spent with the U.S. Army Reserve in Afghanistan. "When you are home adjusting to life, you never expect something like this."
By evening, as the names of victims began to trickle out, families gathered at a nearby hotel to await news.
Around 5:45 p.m., hospitals officials went to the Hampton Inn and released a list of people being treated at Orlando Regional Medical Center and Florida Hospital.
While the news brought comfort to some families, others spilled out into the parking lot screaming.
Jaime Leon's cousin, Luis Wilson, was not on the list. He was told there would be no more information until the following morning.
He came outside furious.
"This is not a plane crash. If he's dead because he's been shot, his ID is in his wallet," he said. "They just need to look and let us know."
Noelia Santiago and her husband, Adrian, waited at the Hampton Inn for information about their nephew Luis Wilson, but heard nothing.
"Our frustration is there is no information," Adrian Santiago said. "They keep bringing food, but there is no information. We'd like to know, is he dead or alive?"
Times reporters Steve Contorno, Kathleen McGrory, Claire McNeill, and Kathryn Varn, reported from Orlando. Times senior news researcher John Martin contributed to this report.