(CNN) -- The gunman who killed 12 people at the Borderline Bar & Grill in Thousand Oaks, California, was a 28-year-old veteran of the Marine Corps who had previous run-ins with the law, officials said.
Here's what we know about Ian David Long so far:
The gunman's body was found in the bar
The shooter is dead, and his body was found inside the bar, police said. He was dead when police arrived on the scene, Ventura County Sheriff Geoff Dean said.
"It's well too early to know if he took his own life," Dean said.
A handgun was discovered
Dean said that officials found a Glock .45-caliber handgun at the scene. The weapon usually holds 10 rounds and one in the chamber, but the gunman used an extended magazine in this shooting, Dean said.
"We have not found any type of assault rifle inside the location," he said.
Dean said he did not know of his motive.
The shooter started firing suddenly
The gunman was dressed in a black trench coat and wearing glasses when he walked into the bar filled with people enjoying a night of line dancing.
"I started hearing these big pops. Pop, pop, pop. There was probably three or four, I hit the ground," John Hedge told CNN affiliate KABC.
Holden Harrah told CNN the gunman opened fire within seconds.
"This guy just came out of nowhere and came out with a gun and shot people in Thousand Oaks, California," Harrah said. "And that's what's really blowing my mind, it's a really safe area."
Reports of the shooting came in around 11:20 p.m. PT.
"I heard a gunshot, I turned around and I saw him shoot a couple more times," California Lutheran University student Teylor Whittler told KABC. "Within a split second, everybody yelled 'get down,' " she said.
Witnesses said that people dropped to the floor and hid behind bar stools in stunned silence. Others jumped over chairs and broke windows to get out of the bar.