(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.

The gunman had previous run-ins with the law.

Police had several contacts with Long previously.

In April, officers responded to a disturbance at Long’s home, and he was somewhat irate and acting irrationally, Dean said. A mental health specialist met with him and ultimately decided not to detain him under laws pertaining to his mental health.

The gunman was on active duty with the US Marine Corps from August 2008 to March 2013, according to Defense Department records.

The gunman started firing suddenly

The gunman was dressed in black 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.

The shooter in last night’s bar shooting was once a student at California State University Northridge. In a statement from University President Dianne Harrison, she said that Ian David Long last attended the school in 2016.

Here’s the full statement:

On behalf of California State University, Northridge, our hearts and thoughts are with the victims, survivors, first responders and loved ones affected by the horrific massacre that occurred in Thousand Oaks last night. 

We have learned that the reported shooter is a former CSUN student, who last attended in 2016.

I know that many in the community have been impacted by this terrible tragedy. I ask that faculty and supervisors be supportive and considerate of anyone who has been touched by this tragedy. Also, please know that University Counseling Services has people available at (818) 677-2366 if you or someone you know need assistance or support. As members of the Matador family, 

I ask that our campus come together and support one another during this troubling time.

 Please check CSUN.edu for updates as more information becomes available.
In accordance with a proclamation issued by the White House, I have directed that U.S. flags on campus fly at half staff until sunset, Nov. 10, in honor of the victims of this senseless tragedy.
Again, I

 share my deepest condolences and sympathies with those affected by this horrific massacre.

The gunman lived with his mother

Dean said that investigators were seeking a search warrant to look through Long’s house, where he lived with his mother.

A neighbor told CNN that Long’s mother “lived in fear” of what her son might do, saying when police were called to the house earlier this year “it took them about a half a day to get him out of the house.”

Neighbor Richard Berge said Long’s mother told him she was concerned about her son, though not worried about her own safety, and that “she was … kind of beside herself, she didn’t know what to do because he wouldn’t get help.”

Berge said that when he saw police activity at the house Thursday morning, “I knew what it was.”

Another neighbor, Gareth Crites, said he rarely saw Long at the house. Crites would wave, but Long wouldn’t wave back, he told CNN affiliate KABC.

Shooter posted online about his military service

California bar shooter Ian David Long posted information about his military service on a special forces forum called Shadowspear in March 2017.

In his post, Long said he had served in Afghanistan, was an infantry machine gunner in the US Marine Corps for four and a half years, and was an instructor in Okinawa.

Here’s part of what he wrote:

“I was honorably discharged in 2013. I am graduating with a B.S. in Athletic Training in two months. I found out a little too late that just wasn’t the job for me. Maybe the ego got the better of me but it took only one time for a 19 year old D-2 athlete to talk down to me and tell me how to do my job that I realized this wasn’t the career I wanted to head.”

CNN also spoke to a friend who served with Long, who confirmed the suspected gunman had served in Afghanistan and moved to southern California to pursue a degree in sports medicine.