News 6 is learning on Tuesday new details about the mass shooting inside Pulse nightclub from a bouncer inside of the club.
Imran Yousef was making his final rounds Sunday when he got caught in the middle of the gunfire.
"Shots go off..." Yousef said. "The initial one as three or four. That was a shock. Three of four go off and you could tell it was a high caliber. Everyone froze. I'm here in the back and I saw people start pouring into the back hallway and they just sardine pack everyone."
It was after that that police say an off-duty officer returned fire and called for backup.
"Because of that exchange of gunfire, that forced the suspect to retreat backwards, stop shooting and retreat backwards into the bathroom where he held some people hostage we believe," said Orlando Police Chief John Mina.
Police say it was then that Omar Mateen called 911 and pledged allegiance to ISIS.
"We were receiving text messages and information from officers and people inside the club that he had explosives, that he was going to start putting on bomb vests on four people, and so we believe based on the information we had loss of life was imminent, so we set up an explosive breach on the other bathroom where the other 15 people were," Mina said.
Bu the police explosive didn't break through, so they rammed into the club with an armored car.
Moments later, Mateen was taken down by police.