Gunfire replaced the blaring music. Glass shattered. People screamed. The acrid smell of gunpowder filled the air.
"Please don't let this be where I go," Casiano prayed.
Casiano froze, certain the gunman was inches away. A figure loomed outside the stall door.
The shots sounded louder. They were getting closer. A man outside the stall collapsed in a pool of his own blood.
Casiano heard a laugh. The sound of "pure evil," he said. "It didn't sound like a person."
The gunman, later identified as Omar Mateen, didn't utter a word. There was another bloodcurdling laugh.
"It was like a laugh of satisfaction," Casiano told CNN's Anderson Cooper.
Mateen fired a round into the stall door.
"Please, please, please don't shoot!" some victims pleaded.
"Please don't do this. Let us go!"
Mateen aimed his pistol over the bathroom stall and opened fire. Casiano was hit twice and fell over. Many of those he hid with were killed.
Satisfied with the silence, the gunman left.
"One of the first things I hear when I close my eyes are guns, bullets hitting the floor and that laugh," Casiano said.
In a bathroom stall: 'blood was everywhere'
It was Patience Carter's first trip to Florida, and Pulse came up in a Google search of Orlando nightclubs.
"We just went from having the time of our lives to the worst night of our lives all within a matter of minutes," Carter told reporters Tuesday.
Like so many others, Carter and her friends also took cover in one of the handicap bathroom stalls.
"People are getting hit by bullets, blood was everywhere," she said.
At one point, she said, Mateen stopped shooting to fix his jammed assault rifle. Hours passed. The gunman would not leave the bathroom.
Carter and others hiding in the bathroom heard Mateen dial 911 and say he's "doing this is because he wants America to stop bombing his country." (Mateen's parents are from Afghanistan. He was born in New York.) He also pledged his allegiance to ISIS.
Her account offered a clue at what the gunman said motivated him to carry out the deadliest mass shooting in American history.
Mateen asked if there were African-Americans in the stall. One man said there were six or seven.
"I don't have a problem with black people," Mateen said, according to Carter. "This is about my country. You guys have suffered enough."
Mateen also claimed to have "snipers outside" the club, Carter said.
"It sounded as if he was communicating with other people who were involved with it ... Maybe he was just deranged, maybe he's just talking to himself, but I honestly feel like I don't think he was able to pull that off all by himself," Carter said.
Some people were rescued after a window air conditioning unit was removed. Dozens also ran to safety when SWAT officers used explosives and construction equipment to breach walls in the club.
Carter said she heard three blasts. She could see the gunman's feet and hear officers telling people to move away from the walls. A broken pipe started to flood the bathroom, the water mixing with pools of blood.
Carter heard the gunman shoot someone. He fired another shot and a man in front her took the bullet. One of her friends was on the ground motionless.
"I was begging for god to take the soul out of my body," she said.
A SWAT team member lifted Carter, who had a bullet wound in her leg, onto the street and dragged her to safety.
In the hospital, she composed a poem that starts, "The guilt of feeling grateful to be alive is heavy."
"I feel guilty about screaming about my legs in pain because I could feel nothing/Like the other 49 who weren't so lucky to feel this pain of mine," she wrote.
One of her friends was wounded but survived. Another was killed.
Out in the courtyard: 'bodies already on the floor'
Samuel Maldonado was working in the club's courtyard, where a crowd was running from inside Pulse. The DJ stopped the music. Gunshots rang out.
A young woman emerged, covered in blood. The gunman continued shooting at her until she collapsed near Maldonado's feet.
Maldonado and his partner hit the ground. They hid under tables. When the shots stopped for a moment, his partner bolted for an exit.
Maldonado, too, tried to run, but there was Mateen, weapon at his side, moving out into the courtyard. So, Maldonado jumped under another table.
"There was this young lady right there, and she was nervous, ranting, screaming, crying," he said.
Maldonado jumped on her and covered her mouth to stifle her cries. The gunman moved closer. He was reloading and turned around toward the club. The shooting resumed.
"You would just see the bodies already on the floor," Maldonado said. "They were literally just jumping."
Mateen kept shooting at people on the ground -- "bop, bop, bop and you would see the bodies just jumping inside."
He moved silently, spreading death
The first shots broke out around 2 a.m. It was almost closing time.
Some 300 or so people had crowded the club early Sunday morning. Many were dancing under flashing strobe lights. Shot boys served $5 skybombs.
Mateen entered the club from the back of the building, armed with an AR-15-type assault-style rifle and a Glock 9mm semiautomatic pistol.
He first headed to the most crowded part of the club, the main bar area. That's where the massacre began.
The loud music blaring from the speakers and the darkness of the dance floor compounded the confusion.
Mateen carried out his killing spree, moving around like a man familiar with the club.
Chris Callen, a performer, said he'd seen Mateen
at Pulse before. Mateen was "very friendly." He seemed comfortable there. Callen estimated the killer regularly visited the club twice a month for about three years.
When it began: hugs, laughter, last calls
Angel Colon said the night started as a great time. By 2 a.m., people were saying goodbye. There were hugs, laughter, last calls. Then the nightmare started.
"We just grabbed each other. We started running."
Colon was shot several times in the leg. He went down and took two more shots. The gunman fired at a woman next to Colon.
"He's shooting everyone that's already dead on the floor, making sure... I'm thinking, I'm next, I'm dead," he told reporters Tuesday.
Mateen aimed at Colon's head, but the bullet struck his hand. Another bullet entered the side of his hip. People were stepping over him.
"It's still fresh to me," he said.
Others dove to the floor, crawling for cover. Some lunged for the doors, separating from friends, stepping over strangers.
Luis Burbano and his best friend ran to an employee access door. The shots were getting closer. He never looked back.
"That'd be the last thing I would see, the last memory I have."
Ray Rivera, a DJ at the club, was playing on the patio. People were barreling out from the club.
A man and a woman dashed under his DJ booth to hide.
"The guy took off and the girl was down there panicking, and I told her she needed to be quiet and as soon as there was a break in the shots, I pushed her and said, "Let's go.'"
Last texts to loved ones
Rivera and the woman bolted to safety. but others weren't as fortunate.
For three harrowing hours, as the gunman took hostages, people crouched in a dressing room or in the air conditioning vents. One woman survived by covering herself with bodies in a bathroom.
Helpless, trapped, shocked and scared, they texted loved ones.
Eddie Jamoldroy Justice, a 30-year-old accountant, sought shelter in the bathroom. He texted his mom:
Mommy I love you
In the club they shooting
Trapp in the bathroom
Im gonna die
His mother, Mina Justice, tried to reassure him that she'd called 911 and help was coming:
Calling them now.
U still there?
Answer your phone.
Call them mommy
Im still in the bathroom
Im going to die
He then went silent. Justice was among the 49 who didn't make it.
Authorities used explosives to get into the club. The first officers inside stepped gingerly over the sprawl of bloody bodies, calling out, "If you're alive, raise your hand
All around, unanswered cell phones chirped incessantly.