NEWBURY PARK, California—Ian David Long, the 28-year-old man accused of the shooting rampage at a southern California bar that killed 12, was found not to be a threat following a visit by police to his home that included questions about whether he suffered from post-traumatic stress syndrome, authorities said.

Police, who are in the early stages of combing through Long’s past, were called to his home in April and found him “somewhat irate and acting a little irrationally,” according to Ventura County Sheriff Geoff Dean.

A crisis-intervention team and a mental health specialist were summoned to assess Long’s mental state, and they discussed whether he had suffered from post-traumatic stress disorder from his time in the U.S. Marine Corps, Dean said. Officers determined he was not a danger to others or himself and did not need to be admitted for further evaluation or treatment.

“The mental health experts cleared him that day,” Dean said, adding that there was nothing to indicate he would go on to commit mass murder. “Obviously he had something going on his head that would cause him to do something like this. So he obviously had some sort of issues.”

As authorities tried to determine a motive for the mass murder, details of Long’s background began to emerge. A high school baseball coach said he seemed a “little strange” and sad. Neighbors said Long lived with his mother and was aloof.

One neighbor, Tim Tanner, recalled the night in the spring that police came to his home. “There were loud banging noises and just a lot of commotion,” he said.

Long's other interactions with include a report in which he was the victim of battery at a local bar in 2015—but not the one he attacked, Borderline Bar & Grill in Thousand Oaks, Dean said.

Late Wednesday, Long pulled up to the Borderline in a vehicle belonging to his mother, armed with a legally purchased Glock .45-caliber handgun that is capable of holding 11 bullets and an extended magazine. It was not clear if the magazine was legally purchased. Police were working to determine how many bullets the magazine can hold.

Speaking with reporters Thursday morning, Dean said a preliminary investigation determined that Long walked up to the bar and first opened fire outside, shooting a security guard.

As he made his way inside, Long shot other security and employees before turning the gun on about 200 people who were inside the bar for a country-music event for college students 18 and over.

Long then opened fire on sheriff's deputy Sgt. Ron Helus, the first arriving officer on the scene, killing him. The second wave of officers found Long dead inside an office located just inside the main door with what authorities say was likely a self-inflicted gunshot wound.

Investigators were combing Long’s background and social media presence for clues. Officers secured Long’s home and the car he drove to the bar while they waited for a search warrant.

Police were investigating claims from multiple witnesses that Long set off a smoke bomb during the rampage. It was not clear how many bullets Long fired or if he reloaded his gun during the shooting, Dean said.

Witnesses said Long was dressed all in black, and Dean confirmed he was wearing a black sweater. He was carrying no identification, so police worked through the night to identify him.

While there was no indication why Long picked Borderline or that he was specifically targeting someone there, Long is a resident of nearby Newbury Park, Dean said, and “common sense would speculate there is some reason he went here and knew about it.”

Outside Long's home, Doug Konzen, who lives nearby, said his sister Kirstal was working her shift as a bartender at Borderline on Wednesday night. Kristal was near a pool table when the shooting started and escaped by going out a window to safety.

“If she had been by the stage, she wouldn’t have been so lucky,” Konzen said.

Kristal, 30, cut her hand and was taken to the hospital where Konzen said he would be visiting shortly. First, though, he just wanted to see the house of the man who nearly killed her, remarking, “I can’t believe this asshole lived down the street from me.”

Long moved to Ventura County from Orange County in his junior year of high school and played one season on the Newbury Park High School baseball team, former head coach Scott Drootin said.

“ He wasn’t a happy-go-lucky person at all. To me it looked like he was a sad person. And I would try to make him smile and he kind of never really did. ” — Former high school coach Scott Drootin

Drootin described Long to The Daily Beast as quiet and reserved but said he was respectful and worked hard as an outfielder.

“I know that we had a feeling he was going to be a military type,” Drootin said. “He always wore a military jacket when he got dressed and went home. He wasn’t a very happy kid. I just remember that I knew someday he was going to be somewhere in a military uniform… You just got that impression.”

Long’s teammates “thought he was a little strange,” so they didn’t really hang out with him, Drootin said.

“He wasn’t a happy-go-lucky person at all. To me it looked like he was a sad person. And I would try to make him smile and he kind of never really did.”

Long’s page in the team’s 2007 media guide said his goal was to play college baseball and then go pro. Under the section for what he planned to do after baseball, Long wrote: “Death.”

Long enlisted in the Marines in August 2008. He was deployed to Afghanistan from November 2010 to June 2011, and left the military in March 2013.

After he left, Long posted periodically on a forum for military members, according to posts reviewed by The Daily Beast and first reported by NBC News. In a 2012 post, Long described his long-term goal of becoming a Navy SEAL (it’s unclear if he tried). In 2017, Long returned to the forum after a hiatus and wrote about trying to go to school for a degree in athletic training before he grew discouraged.

“I found out a little too late that just wasn’t the job for me,” he wrote. “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.”

In the same 2017 post, he said he was “waiting (and training) to return to the military,” though he did not.

California State University at Northridge confirmed Thursday that Long had been a student there, but he stopped taking classes in 2016 and did not graduate.

Long lived with his mother on a street lined with palm trees, an American flag wrapped around a flagpole on the garage and a green outdoor light symbolizing support for veterans. The mother was often seen walking three German shepherds.

A SWAT team showed up at the house around 5 a.m. and gave her the news, neighbors said. She then left the area and has not made a public statement about the shooting.

Later in the day, a local woman who did not give her name came by with a small bouquet of flowers that she left on the lawn. “He was a Marine like my son,” she said. “I am here to support the mom. She needs to know she has support too.”

—With additional reporting from Spencer Ackerman and Kelly Weill