THOUSAND OAKS, Calif. (AP) — Terrified patrons hurled barstools through windows to escape or threw their bodies protectively on top of friends as a Marine combat veteran killed 12 people at a country music bar in an attack that added Thousand Oaks to the tragic roster of American cities traumatized by mass shootings.

Dressed all in black with his hood pulled up, the gunman apparently took his own life as police massed at the Borderline Bar & Grill in Southern California.

The motive for the attack late Wednesday night was under investigation.

The killer , Ian David Long, 28, was a former machine gunner and Afghanistan war veteran who was interviewed by police at his home last spring after an episode of agitated behavior that authorities were told might be post-traumatic stress disorder.

Opening fire with a handgun with an illegal, extra-large magazine, Long shot a security guard outside and then went in and took aim at employees and patrons, authorities said. He also used a smoke bomb, according to a law enforcement official who was not authorized to discuss the investigation publicly and spoke on condition of anonymity.

Survivors of the rampage — mostly young people who had gone out for college night at the Borderline, a hangout popular with students from nearby California Lutheran University — seemed to know what to do, having come of age in an era of active-shooter drills and deadly rampages happening with terrifying frequency.

Several of the survivors said they were also at the outdoor country music festival in Las Vegas last year when a gunman in a high-rise hotel killed 58 people.

Many of the hundreds of patrons dived under tables, ran for the exits, broke through windows or hid in the attic and bathrooms, authorities and witnesses said.

“Unfortunately our young people, people at nightclubs, have learned that this may happen, and they think about that,” Ventura County Sheriff Geoff Dean said. “Fortunately it helped save a lot of lives that they fled the scene so rapidly.”

Matt Wennerstrom said he pulled people behind a pool table, and he and friends shielded women with their bodies after hearing the shots. When the gunman paused to reload, Wennerstrom said, he used a barstool to shatter a window and then helped about 30 people escape. He heard another volley of shots after they got out.

“All I wanted to do was get as many people out of there as possible,” he told KABC-TV. “I know where I’m going if I die, so I was not worried.”

The dead included a veteran sheriff’s deputy who rushed in to confront the gunman, as well as 22-year-old man who planned to join the Army, a freshman at nearby Pepperdine University and a recent Cal Lutheran graduate.

“It’s a horrific scene in there,” Dean said in the parking lot. “There’s blood everywhere.”

The tragedy left a community that is annually listed as one of the safest cities in America reeling. Scores of people showed up to donate blood for the wounded.

All morning, people looking for missing friends and relatives arrived at a community center where authorities and counselors were informing the next-of-kin of those who died. Many walked past TV cameras with blank stares or tears in their eyes. In the parking lot, people comforted each other with hugs or a pat on the back.

Jason Coffman received the news that his son Cody, 22, who was about to join the Army, was dead. Coffman broke down as he told reporters how his last words to his son as he went out that night were not to drink and drive and that he loved him.

“Oh, Cody, I love you, son,” Coffman sobbed.

It was the nation’s deadliest such attack since 17 students and teachers were killed at a Parkland, Florida, high school nine months ago. It also came less than two weeks after a gunman massacred 11 people at a synagogue in Pittsburgh.

Democratic Gov.-elect Gavin Newsom, in his first public appearance since winning office on Tuesday, lamented the violence that has come again to California.

“It’s a gun culture,” he said. “You can’t go to a bar or nightclub? You can’t go to church or synagogue? It’s insane is the only way to describe it. The normalization, that’s the only way I can describe it. It’s become normalized.”

President Donald Trump praised police for their “great bravery” in the attack and ordered flags flown at half-staff in honor of the victims.

Authorities converged on Long’s home in Newbury Park, about 5 miles from the Borderline bar, in a search for clues to what set him off.

“There’s no indication that he targeted the employees. We haven’t found any correlation,” the sheriff said. “Maybe there was a motive for this particular night, but we have no information leading to that at all.”

Long was in the Marines from 2008 to 2013, rose to the rank of corporal and served in Afghanistan in 2010-11 before he was honorably discharged, the military said. Court records show he married in 2009 and was divorced in 2013.

Authorities said he had no criminal record, but in April officers were called to his home, where deputies found him angry and acting irrationally. The sheriff said officers were told he might have PTSD because of his military service. A mental health specialist met with him and didn’t feel he needed to be hospitalized.

Tom Hanson, 70, who lives next door to Long and his mother, said Thursday that he called the police about six months ago when he heard “heavy-duty banging” and shouting coming from the Longs’ home.

“I was concerned because I knew he had been in the military,” he said.

Hanson said the sheriff’s deputy who arrived took his information, but he never learned more about what happened and hadn’t spoken to Long since then.

Long was armed with a Glock 21, a .45-caliber pistol designed to hold 10 rounds plus one in the chamber, according to the sheriff. But it had an extended magazine — one capable of holding more ammunition — that is illegal in California, Dean said.

Sheriff’s Sgt. Ron Helus and a passing highway patrolman arrived at the club around 11:20 p.m. in response to several 911 calls, heard gunfire and went inside, the sheriff said. Helus was immediately shot, Dean said.

The highway patrolman pulled Helus out, then waited as a SWAT team and scores more officers arrived. Helus died at a hospital.