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Chilling witness accounts describe moment gunman opened fire in California nightclub - 'It looked like he knew what he was doing'

Chilling witness accounts have emerged from the Southern Californian bar where a former US Marine opened fire, killing 12 before taking his own life. 

Using a smoke bomb and a handgun, hooded Marine combat veteran dressed all in black opened fire during college night at the country music bar in Thousand Oaks.

Screaming in fear, patrons rushed for the exits, ducked under tables and hurled barstools to smash second-floor windows and jump to safety as gunfire erupted at the Borderline Bar & Grill, a hangout popular with students from nearby California Lutheran University.

"I dropped to the floor," Sarah Rose DeSon told ABC's "Good Morning America." ''A friend yelled, 'Everybody down!' We were hiding behind tables trying to keep ourselves covered."

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The shooter has been identified as 28-year-old Ian David Long, who also died in the attack. Source: Breakfast

Cole Knapp, a freshman at Moorpark, said he was inside the bar when the shooting began, but he thought at first that it was "just someone with an M-80, just kind of playing a prank."

Then he said he saw the gunman, wearing a small black head covering and black hoodie and holding a handgun.

"I tried to get as many people to cover as I could," Knapp said.

"There was an exit right next to me, so I went through that. That exit leads to a patio where people smoke. People out there didn't really know what was going on. There's a fence right there so I said, 'Everyone get over the fence as quickly as you can,' and I followed them over."

People out there didn't really know what was going on. There's a fence right there so I said, 'Everyone get over the fence as quickly as you can,' and I followed them over."

He said a highway patrol officer who happened to be pulling someone over was nearby.

"I screamed to him, 'There's a shooter in there!' He was kind of in disbelief, then saw that I was serious," Knapp said. He said he had friends who hadn't been accounted for.

Tayler Whitler, 19, said she was on the dance floor with her friends nearby when she saw the gunman shooting and heard screams of "Get down!"

"It was really, really, really shocking," Whitler told KABC-TV as she stood with her father in the parking lot. "It looked like he knew what he was doing."