The dead included 11 people inside the bar and a veteran sheriff's sergeant who was the first officer through the door.
Kelly, a 22-year-old Marine, said he heard "pop, pop" and instantly knew it was gunfire.
A neighbour, who would only identify himself by his last name, Hanson, said Long lived with his mother.
"It's a horrific scene in there", Dean said in the parking lot. "Right now as far as we know there was only one handgun, but that could certainly change as we do a more thorough search of the building".
President Donald Trump praised police for their "great bravery" in the California attack and ordered flags flown at half-staff in honor of the victims.
"I can't tell you what the status of any of those that were shot is at this point", said Ventura County Sheriff's Office Capt. Garo Kuredjian. "We haven't found any correlation", the sheriff said.
The assailant, identified as Ian David Long, a troubled former machine gunner who served a tour in Afghanistan, died of a self-inflicted gunshot wound.
It was college night and country two-step lessons were being offered Wednesday at the Borderline, according to its website.
Law enforcement agencies, firefighters and other first responders, along with several ambulances, additional units from the California Highway Patrol, Simi Valley and the Federal Bureau of Investigation, reached the spot soon after the shooting was reported. Whitler said then she heard "Get up, he's coming!" and people trampled on each other to get out.
Where is my voting location? Where do I go to vote?
Wind gusts could reach 40 to 50 miles per hour as the line of storms moves through this afternoon, Okulski said. Polls will be open from 7 a.m.to 7 p.m. "We will wait on everybody", she said, "who's in line by 7 o'clock".
An unknown number of people were wounded during the attack at the Borderline Bar and Grill, a country & western venue in the Los Angeles suburb of Thousand Oaks. "It's affecting the way I view relationships, because I'm afraid when it comes to the safety and well-being of everyone that I love". The CHP officer retreated, secured the perimeter and then pulled Helus out of the line of fire, KCAL reported. He praised the slain officer - a close friend - as a hero: "He went in there to save people and paid the ultimate price".
"Obviously he had something going on in his head that would cause him to do something like this", Dean said.
"When (he) started to reload, that's when we got people out of there and I didn't look back", Wennerstron said.
Customer Matt Wennerstrom, 20, told several news outlets that once he saw the shooter open fire, he quickly ushered people behind a pool table.
Reflecting on how he would get through his own pain, Jason held on tightly to his father-in-law, Mike Johnston, saying "I love this man".
Another Pepperdine student, Peyton Lee, said the students there can take some comfort in knowing their friend is at peace. "The last thing I said was, 'Son, I love you'".
A few weeks after the Vegas shooting, the bar held a benefit concert for five people from the area who were killed, and now-eerie social media posts show a number of survivors holding up a "Route 91" sign inside the bar at a six-month anniversary event.
Helus was not only a 29-year sheriff veteran, but he was also a husband and father.