Authorities in Thousand Oaks, Calif., Northwest of Los Angeles, reported 13 deaths in a bar and dance hall on Wednesday night after several shots were fired by a man inside.
Ron Helus, sheriff's sergeant, was among the dead. The gunman was also dead inside, officials said.
Ventura County Sheriff Geoff Dean said he had no reason to believe there was a link to terrorism, "but we will certainly see that option."
"It's a horrible incident," Dean told reporters. "It is part of the horrors that are happening in our country and everywhere, and I think it is impossible to put any logic or meaning to the fool."
The sheriff's sergeant, who died at the hospital about an hour after suffering the injury, was a 29-year veteran of the force and expected to retire soon. He was survived by a wife and a son.
In addition to the dead, Dean estimated that there were more than 10 to 12 gunshot victims who were "rescued from the scene and taken to local hospitals." Additional victims of minor injuries have fled on their own, he added.
"I know there are parents asking," Oh my God, was it one of my kids there? Or was it my sister or my brother? "He said.
Reports from a gunman arrived around 11:20 a.m. Pacific Time Wednesday, and deputies arrived at the venue
Special weapons and tactical teams arrived shortly thereafter, along with the FBI. The video of the scene showed the noise seekers taking injured people to medical care vehicles.
By Thursday morning, the building had been emptied, Kuredjian said, adding, "We are confident there are no exceptional marksmen."
A man and his stepfather interviewed by ABC7 Eyewitness News said they had heard about 12 shots before they could walk out the front door of the nightclub.
"He fired the first shot," said his stepfather. "And I knew it was real. My son thought it was a joke, so I pulled him down and got some coverage. I looked up and he was moving to the right. He shot the front porter, who was just a young man. So he shot the box, just a girl.
Multiple witnesses reported having seen smoke, possibly from smoke bombs, and said people used chairs to break windows and escape from the scene.
"It was an absolute panic," said Teylor Whittler, 19, who was inside the scene at the time. "Everyone ran and fell as fast as I could."
She said she ran to the back door, where people were crowding as the shooting subsided. "And then, suddenly, some guys started running to the back door and said," Get up, it comes in. "
Borderline is described as the country's largest dance hall and live music venue. With a dance floor covering about 2,500 square feet, it is open until 2:00 in the morning, five days a week.
Wednesday was "College Country Night" at the bar. Officials said more than 100 were inside the shooting site.
Rochelle Hammons, 24, told The Post he heard four shots before he could flee.
"Suddenly we hear four shots, you know," bang, bang, bang, bang ". Everyone fell on the floor. Everyone bent over and covered themselves, "she said. "When everyone crouched on the floor, I realized that my only chance would be to run to the nearest exit. I saw the nearest exit and ran as fast as I could.
From inside her car, she saw the first officer arrive, she said. She lowered the window and told him that there was an active shooter inside.
"You have to hurry, you have to go in there," she insisted.
The shooting came just over a year after 58 people died at a country music festival in Las Vegas when Stephen Paddock, 64, opened fire on the 32nd floor of the Mandalay Bay Resort and Casino.