"Multiple assets from the ATF Los Angeles Field Division have responded to the mass shooting at the Borderline Bar and Grill in Thousand Oaks", California, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives, via Twitter.
In a press conference early Thursday morning, the Ventura County Sheriff confirmed the gunman was also killed and there is no threat to the community of Thousand Oaks.
"Dean said that the dead police officer, who was named as Ron Helus and had been on the force for 29 years, was among the first on the scene".
Reports say the suspect may have used smoke grenades and at least one gun during the attack which forced people to flee, breaking windows with chairs to escape the shooting.
"It's a horrific scene in there".
"It was just semi-automatic, as many shots as he could pull, and then when it started to reload that's when we got people out of there and I didn't look back".
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Ventura County sheriff's Capt. Garo Kuredjian said hundreds of people were inside the Borderline Bar & Grill in Thousand Oaks at 11:20 p.m., and shots were still being fired when deputies arrived.
TV footage showed SWAT teams surrounding the bar, with distraught revelers milling around and using their cell phones as lights from police cars flashed. Dean said at least 10 additional people were shot and wounded.
A man who says he was in the bar tells ABC news reports that he saw a man shoot into the crowd.
"A gentleman, who walked in through the front door, shot the girl that was right behind the counter", he added. "I don't know if she is alive", he said. California Highway Patrol was on scene within 3 minutes, with first officer to enter shot numerous times.
Nick Steinwender, student body president at nearby California Lutheran University, rushed to the scene when he heard about a shooting at the bar where he knew friends and fellow students were.
The shooter took at least 30 shots.