KABC-TV(THOUSAND OAKS, Calif.) — At least 12 people, including an officer, were killed when a gunman burst into a packed Southern California bar overnight and opened fire, authorities said.The lone suspect, 28-year-old Ian David Long, was found dead inside the Borderline Bar & Grill in Thousand Oaks, Ventura County Sheriff Geoff Dean said. Authorities believe he shot himself.Long, who lived in nearby Newbury Park, was a U.S. Marine Corps veteran, Dean said.His only weapon was a legally purchased .45-caliber handgun, Dean said. Long added an extended magazine to the Glock gun, the sheriff said.Ventura County Sgt. Ron Helus, a 29-year veteran, was among the dead, Dean said.Helus, 54, was one of the first on the scene and was struck multiple times when he entered the building, the sheriff’s office said.The bar was packed when police responded to the country western bar in Thousand Oaks, about 40 miles west of Los Angeles, just before midnight local time.Teylor Whittler was celebrating a friend’s birthday at the bar’s college night when she heard gunshots.“A bunch of people dog-piled on top of each other,” she told “Good Morning America.” “Everyone just yelled, ‘Run, he’s coming!’”“There were at least 50 people that all tried getting up at once and running out the back door. I ended up getting caught in the ground and stumbled over by multiple people,” Whittler said. “I got hit in the head by a stool that was being picked up to throw through a window, until some guy came up behind me and grabbed me and said, ‘Get up, we have to go!’”She said multiple men around her blocked the group with their bodies, “ready to take a bullet for every single one of us.”Whittler’s friend, Sarah Rose DeSon, told “GMA” she was hiding behind a table when she saw a spark and smoke.“As soon as we all saw that, we jumped up,” she said. “I ran out the front door, down some stairs, face-planted in the parking lot but I was lucky enough to get out alive.”“I’m terrified,” DeSon added. “We’re just praying for our friends that we haven’t heard from. … You never think it’s going to be you until it happens. This is a problem. This is real and it’s awful.”“They were very, very loud gunshots,” college student Erika Sigman told ABC Los Angeles station KABC. “There were people in the middle dancing … you hear that and you just know.”“We got down because I heard people screaming, ‘Everyone get down!’” she said. “We heard people say, ‘Run!’ and we booked it as fast as we could.”“I love this place — it’s our usual hangout. My parents trust me going here,” Sigman noted. “It’s very hard to comprehend.”Thousand Oaks ranked third in America’s safest cities this year, according to Niche, a Pittsburgh-based company that researches neighborhoods and schools across the country based on public data as well as resident reviews.The slain sergeant, survived by his wife and son, was looking to retire soon, the sheriff’s office said. Instead, he made “the ultimate sacrifice,” Dean said.When the shooting report came in, the sheriff said Helus was speaking with his wife on the phone.“Hey, I got to go handle a call, I love you,” Helus told his wife, according to Dean.President Donald Trump has ordered flags to be flown at half-staff until Saturday at sunset “as a mark of solemn respect for the victims,” he said in a proclamation.Authorities are working to determine the suspect’s motive.This is a breaking story. Please check back for updates.Copyright © 2018, ABC Radio. All rights reserved.