People threw barstools through window to escape Thousand Oaks, California, bar during shooting

As a gunman dressed in black used a smoke grenade and opened fire at a bar in Thousand Oaks, California, Wednesday, a few people threw barstools through the bar's windows and helped people escape, according to witnesses. 

Matt Wennerstrom, 20, told reporters that he and his friends often visited the Borderline bar and grill, which was hosting a college night when the shooting took place. Wennerstrom said he heard a loud sound, and saw a "tall black figure with a handgun opening fire at the employees working at the front desk." 

"At that point I grabbed as many people around me as I could and grabbed them down under the pool table we were closest to until he ran out of bullets for that magazine and had to reload," Wennerstrom said. 

As the gunman reloaded, Wennerstrom said he and a few others started throwing barstools through the window and "shuffling as many people out as possible." 

Twelve people were killed, including a sheriff's sergeant. The shooter, identified by authorities as Ian David Long, 28, apparently fired at random, and died at the scene.

Sarah Rose DeSon told Good Morning America that the gunman appeared to throw a smoke grenade inside the bar. 

"As soon as we all saw that, we jumped up," DeSon told GMA. "I ran out the front door, down some stairs, face-planted in the parking lot, but I was lucky enough to get out alive."

Cole Knapp, who said he goes to Borderline each week, told AP he thought the shooting was someone "playing a prank.”

“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.”

A law enforcement official told The Associated Press the suspect was 29 years old, armed with a .45-caliber handgun and used a smoke device. The official declined to provide any other details, speaking on condition of anonymity for lack of authorization to publicly discuss the investigation.

More:Sheriff’s sergeant, 11 other victims dead in Thousand Oaks, Calif., bar shooting

More:'He died a hero': Ventura County Sheriff Sgt. Ron Helus among those killed in bar shooting

Wennerstrom, who had blood on his shoulder, said he and his friends continued to help people once they left the bar. 

"At that point there was a couple of people carrying a guy out who had been shot .... and they were getting fatigued so a few of us took over, and this is his blood," Wennerstrom said.

Contributing: Joe Curley, Ventura County Star; Mary Bowerman, USA TODAY