Long, a 28-year-old who had spent several years with the Marines and served in Afghanistan, was acting somewhat irate and a little irrationally, according to Ventura County Sheriff Geoff Dean.
A mental health specialist with the crisis team met with him and felt he might be suffering from post-traumatic stress disorder. But after speaking with him, they decided not to detain him under laws that allow for the temporary detention of people with psychiatric issues.
Seven months later, officers swarmed his home again for a very different reason: a mass shooting.
Long was identified by police on Thursday as the gunman who killed 12 people and injured more than a dozen more in a sudden spree of violence at the Borderline Bar & Grill in Thousand Oaks.
Survivors of the shooting said the gunman, dressed in black and wearing glasses, shot a security guard outside and then shot a young woman working at the counter just inside the door before opening fire on others.
One of the victims, Ventura County Sgt. Ron Helus, was fatally shot when he entered the bar and tried to stop the rampaging gunman, Dean said.
Police then regrouped and, after waiting for reinforcements, were able to enter the bar. Inside, they found Long dead of what Dean said he believed to be a self-inflicted gunshot.
One handgun, a legally purchased .45-caliber Glock, was found at the scene. The weapon usually holds 10 rounds, plus another in the chamber, but the gunman used an extended magazine in the shooting, Dean said.
He was a frequent visitor to the bar
On Thursday morning, Dean said he did not know of the shooter's motive, and he did not know of any connection between Long and the Borderline bar.
But friends told CNN that Long frequently visited the bar.
"We would go to Borderline together. He really liked it," said one woman who has been friends with Long for five years and does not want her name made public.
"I would make fun of him, because he would drag me there. Sometimes we'd go there to have a drink, sit and talk, listen to music," she said.
Borderline, a Western-themed establishment known to regularly host country, salsa and swing dancing nights, was hosting a college country night on Wednesday evening.
"There was a community there. He was a part of that community. The whole bar is line dancing. People do choreographed dances for hours, cowboy boots and hats in the middle of the suburbs of Thousand Oaks," the friend said.
A person who was a childhood friend of Long's until their early 20s and who does not want their name revealed publicly similarly said they used to go to Borderline together. The friend expressed shock that Long would do such a thing.
"I don't know what the hell happened. He was always happy. I never thought this would ever come from him. We used to go snowboarding all the time. He was a good guy," the friend said.
A third friend who does not want to be publicly identified said Long stopped communicating two years ago but said the shooting was unlike him.
"He wasn't unhinged, he wasn't violent. He was a sweet guy who served his country and was using his GI Bill to go to college and get a degree to help more people," the friend said. "Out of our group of friends I thought the highest of him. This is just horrible and I'm so sorry for the victims and his family."
He was in the Marine Corps
The gunman was on active duty with the US Marine Corps from August 2008 to March 2013, according to Defense Department records.
He posted information about his military service on a special forces forum called ShadowSpear in March 2017.
Under the name "doorkicker03," Long said he had served in Afghanistan, was an infantry machine gunner in the Marine Corps for 4½ years, and was an instructor in Okinawa in Japan.
"I was honorably discharged in 2013. I am graduating with a B.S. in Athletic Training in two months," he wrote in the post. "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."
Long did not complete his degree. He was a student at California State University, Northridge, majoring in athletic training from 2013 to 2016, but he did not graduate, university representative Carmen Ramos Chandler said.
"He had a great sense of humor and like most Marines who have seen combat it could get dark at times, just like all of us," Kellogg said.
"He was excited to get out so he could go back home, ride his motorcycle again and finish school."
Long was married in 2009 in Honolulu, but separated in 2011 and dissolved the marriage in April 2013 in Ventura County, California. He and his then-wife said they had no children and owned no property.
A settlement agreement stated, "Irreconcilable differences have caused the irremediable breakdown of our marriage."
He 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 people dropped to the floor and hid behind barstools in stunned silence. Others jumped over chairs and broke windows to get out of the bar.
He lived with his mother
FBI Assistant Director Paul Delacourt said agents are processing Long's home and vehicle in an effort to identify his motivation and paint a picture of his frame of mind. There are no indications Long was working with any associates, he said.
A neighbor said 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 when he saw police activity at the house on 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.