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Norman Casiano froze, certain that the gunman was standing inches from him.

Casiano and dozens of other patrons at the Pulse Nightclub had crammed into a bathroom stall to hide from the shooter. And now, there was a figure looming right outside their bathroom stall door.

More shots rang out. Then the person standing in front of the stall collapsed.

“It was another patron of Pulse, and he was bleeding,” Casiano said. The victim had been shot while looking for a place to hide. Casiano glanced at the floor to see a pool of blood spreading.

Then, he heard it — a laugh.

“It didn’t sound like a person,” Casiano said of the gunman. “He didn’t speak. The only sound we heard was the laugh.”

To Casiano, it was the sound of “pure evil.”

“That’s what it sounded like. It was like a laugh of satisfaction like ‘I’m doing what I came here to do,'” he told CNN’s Anderson Cooper.

Gunman moved silently, spraying gunfire

The first shots broke out around 2 a.m.

The gunman, Omar Mateen, had 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 where he unleashed gunfire. From there, he carried out his killings silently throughout the club. It appeared he may have been familiar with the club long before he entered Sunday morning.

Chris Callen, a performer who’d worked at Pulse, told CNN he’d seen Mateen a couple times at the nightclub. Callen said he once introduced himself and Mateen was “very friendly” and that he seemed comfortable there. Mateen would regularly come to the club twice a month for a period of three years, he estimated.

Four regular patrons at Pulse also told the Orlando Sentinel they had seen Mateen there multiple times.

Victims’ pleas met with no mercy

As the gunman sprayed gunfire through the crowded bar, clubgoers ducked to the ground. Glass shattered around them and the music shut off.

Witnesses could hear the continuous spray of gunfire then a pause as Mateen reloaded his gun.

Mateen left the main bar area and went into an area of the club with dressing rooms and bathrooms.

Just minutes before the gunman approached, Casiano had crawled into the bathroom and wedged himself into a stall, crammed with 20 to 30 people. They were hiding, crying and saying prayers under their breath.

“Please don’t let this be where I go,” Casiano prayed.

The gunshots got louder and closer. And that’s when he heard the shooter’s bloodcurdling laugh over his latest victim.

The shooter approached the bathroom stall where Casiano was hiding and fired a round into the door. As the victims inside were peppered with bullets, they begged: “Please, please, please don’t shoot!”

“Please don’t do this. Let us go!”

The gunman responded to the pleas by aiming his pistol over the bathroom stall and spraying more bullets. Casiano got hit with two bullets and fell over. Many inside the stall died, he said.

The gunman, satisfied with the silence, left.

Casiano has been released from the hospital, but has since struggled with the traumatic sounds reverberating through his mind.

“One of the first things I hear when I close my eyes are guns, bullets hitting the floor and that laugh.”

CNN’s Tom Foreman and Anderson Cooper contributed to this story.

By Madison Park