3 Hours of Horror: Inside the Orlando Nightclub Massacre

— -- "Orlando," as he prefers to be known, walked with a female companion from the lounge area of Pulse to the area of bathrooms at a little before 2 a.m. on Sunday. He told ABC News they heard "popping sounds" layered on top of the Latin dance music that drifted through the bathroom walls.

Orlando's friend said she thought the noises were part of the music, but the sound arrived in sporadic intervals that grew louder over time. They positioned themselves with their legs above the bottom of the stall at first to give the appearance of a vacant space. He said they heard other club-goers enter a neighboring stall, driven there by a killer who opened fire on them, eliciting screams from the unseen crowd. According to Orlando, he and his friend stayed in that position, hovering above the floor, until a young black man crawled under their stall and grasped for them.

Not wanting the man to tip off the killer, Orlando said they slunk to the ground to play dead. He remained with his face pressed against the toilet, listening to his phone ring in repetition with calls and messages from loved ones. He described hearing the commotion get louder and closer -- until police killed the shooter, Omar Mateen, who had, by then, murdered 49 people while invoking the name of ISIS. It was the worst mass shooting in U.S. history.

Details of Sunday's massacre have so far centered around 2 a.m. and 5 a.m., the approximate times at which Mateen entered the club shooting and was shot by police.

But, the three-hour period when hostages were held in the club and when Mateen spoke on the phone with police, pledging allegiance to ISIS and declaring solidarity with other prominent terrorist figures, are now starting to emerge.

2 a.m., Gunshots are heard

The sound of gunshots announced the presence of Mateen to club-goers.

Chris Hansen, a club-goer, was heeding the bartender's announcement for last call by ordering drinks when he heard the shots. Like Orlando's female friend, he mistook it for part of a song.

Brandon Wolf told ABC News that he was also in one of the bathrooms at the time the shooting began. He ran for the front door, and made it outside, where he heard the shots continuing "for minutes" inside the club.

Joshua McGill told ABC News that he was at the club with his roommates when the shooting started. He never saw Mateen, but he heard his weapon.

"It was just a loud sound, so we didn't know what it could have been," he said.

McGill and his friends managed to duck out the club's backdoor. They hopped a fence and fled before returning to help the wounded. Pulse posted a message on their Facebook page at 2:09 a.m. telling people to run.

Amanda Alvear, a club-goer, posted a Snapchat video of her night at the club that her brother Brian Alvear shared with ABC News showing a timeline of her night, starting with images of her drinking and dancing, enjoying "Latin night" with friends.

The video concludes with the sound of gunfire crackling through the air and Alvear looking frightened.

Hansen, Wolf, and McGill survived the attack. Alvear has been listed among the dead.

According to Orlando's account of events, Mateen moved through the club, shooting in bursts, before moving a group of hostages into two bathrooms.

The Orlando Chief of Police said in a press conference today that the hostages were split into two groups, positioned in each bathroom. One group contained 15 to 20 hostages. The second group contained Mateen, as well as four or five other hostages.

Two of the hostages in Mateen's room were Orlando and his friend.

Inside the hostage situation

Orlando told ABC News that he heard Mateen tell people not to call the police or text. He said that he asked hostages in the bathroom what their race was, and told people who answered "black" that he didn't have "an issue" with blacks. After that, Orlando said, he called someone on the phone and said he wanted America to "stop bombing ISIS in Syria."

According to the FBI, the "someone" at the other end of the call was likely police. The FBI told reporters today that Mateen spoke with police three different times from the club during the attack, which started at about 2:30 a.m. on Sunday. He called and hung up, called again and spoke with a dispatcher. The dispatcher then returned his call, according to the FBI.

Mateen was "cool and calm" during their conversations, according to police, and didn't make any demands. He pledged allegiance to the terror group ISIS and referenced the 2013 Boston Marathon bombers, Tamerlan and Dzhokhar Tsarnaev, officials said. He also referenced U.S. suicide bomber Moner Abusalha.

In a statement made yesterday afternoon, the FBI said Mateen had been interviewed by them in 2014 because of alleged ties to Abusalha. Abusalha, son of a Palestinian father and American mother, also grew up in Florida, where his friends called him "Mo.” On May 25 2014, at the age of 22, Abusalha died while driving a truck packed with explosives into a government outpost in Syria and detonating the charge.

Orlando told ABC News that Mateen mentioned on the phone that other people were involved in his plot, and that "snipers" were outside. But, according to officials, Mateen acted alone.

He said he heard shells hit the ground and Mateen say "I've got plenty of bullets." Later, he shot more people in the bathrooms.

At one point, Orlando said that he heard cops screaming "get down."

Decision to move in

The Orlando Police Department decided to move on the club when Omar Mateen threatened to begin putting bomb vests on hostages. Around 5 a.m., they drove an armored vehicle through one of the bathroom walls, penetrating the building's exterior. They also threw "distraction devices," which released sound and light.

Mateen exited the hole made by officers along with some of the hostages. He engaged in a gun battle with officers and was killed.

Thirty people were rescued from the club alive, police said. At least 49 people were killed, not including Mateen. At least 53 people were wounded in the attack.

Orlando said he heard explosions as the hostage situation drew to a close around him. Police pulled him out of the club. ABC News asked him about the friends he lost inside. He claimed that he knew 75 percent of the patrons, and that he thought of his friends every time he heard a gunshot.

"May God be with them, may God bless their soul," he said, choking back a sob.