While authorities have not named all 12 victims in the shooting, a father of one person who died identified his 22-year-old son as among those who were killed. He says Helus was later declared dead at a hospital. Police said the gunman was also dead when officers arrived at the scene. "He went in to save lives, to save other people".
A neighbor, Tom Hanson, told local television station KTLA that he and other neighbors knew Long "had issues".
Ventura County Geoff Dean addresses the media about the shooting at the Borderline Bar and Grill in Thousand Oaks, Calif., Nov. 8, 2018.
The Borderline, which opened in the 1980s, calls itself "Ventura County's largest country dance hall and live music venue" with 2,500 square feet of wide-open dance floor, according to its website. Nine months ago, another mass shooting occurred in Parkland, Florida, where 17 students and teachers were fatally shot at Marjory Stoneman Douglas High School.
A US official told NPR's Tom Bowman that Long "was not a stellar Marine".
Dean said Long had previous run-ins with police, including one instance in April where he acted "a little irrationally".
It was "college night" at the bar, and many students were there to learn the country two-step.
When the shots started, some people smashed windows with chairs to escape, witnesses told CNN.
A man and his stepfather interviewed by ABC7 Eyewitness News said they heard about a dozen shots before they were able to flee out the front door.
An undated photo of Ventura County Sheriff Sgt. Ron Helus, who was shot and killed in a mass shooting at a Thousands Oaks, Calif., bar, November 7, 2018. "I love you. I'll talk to you later". Another witness said the gunman wielded what looked like a sub-machine gun.
One survivor, Matthew Estron, told NBC Los Angeles that the shooter was tall dressed "all in black" and armed with a handgun and some kind of smoke grenades.
Cody Coffman, 22, went to the Borderline Bar and Grill most Wednesday nights to line dance.
The deadliest attack in modern USA history came last year in Las Vegas when a 62-year-old man opened fire on a crowd of 22,000 country music concertgoersfrom the 32nd floor of a nearby hotel, killing 58 and wounding hundreds. "I don't know if she is alive", he said.
A man who says he was in the bar told ABC news that he saw a man shoot into the crowd of customers - many of whom said to be students.
The incident happened at the Borderline Bar and Grill, about 40 miles north of LA.
"A lot of people were just running around, young kids, and I just heard the gunshots going even as I was running to the auto", Dominguez said while fighting back tears.