Updated at 9 a.m. ET

A gunman killed 12 people and injured several more at a country music bar in Ventura County, Calif., late Wednesday, police said. When the shooting started, the Borderline Bar & Grill in Thousand Oaks likely held hundreds of people, drawn by College Country Night.

The dead include Sgt. Ron Helus, a 29-year veteran of law enforcement who died at a nearby hospital, Ventura County Sheriff Geoff Dean told reporters early Thursday.

After the shooting was reported around 11:20 p.m. local time, Helus, 54, entered the building along with a highway patrol officer and was shot multiple times.

"He died a hero. He went in to save lives, to save other people," Dean said. He also said the sergeant had been slated to retire next year.

Describing the gunman's actions, the sheriff told NPR, "He shot a security guard outside, and went inside and continued to fire, and killed 11 people inside."

All of the victims seemed to be from 19-25 years old, Dean said. Investigators are still working to identify them, and families have not yet been notified.

When police entered the bar, they found a "horrific scene," Dean said.

Police found the shooting suspect dead inside, the sheriff said. He added that the suspect had not yet been identified, and a motive was not known. The FBI is assisting with identifying the man, Dean said. Witnesses have described him as tall and dressed in all black, wearing a hood.

There were 10-12 people injured inside the bar, Dean said, and other people who had minor injuries left the scene on their own. The Borderline is popular with students from Pepperdine University — which says it has confirmed "multiple" students were there Wednesday night.

The university is holding classes as normal on Thursday, it says in an emergency bulletin. It adds that students can "adjust their class schedules today" if needed.

"I heard something go off — obviously, the gunshots," witness Erica Sigman told NPR's Kirk Siegler. "And I realized that it was not music very very quickly. And I heard everyone scream, 'Get down!' I heard people start saying, 'run.' So I booked it to my car and with a group of people. ... And hid behind my cars for a little bit. It stopped and then there was a second round that went off."

Another witness told ABC 7 that he saw a suspect throw smoke bombs into the front of the restaurant and shoot a security guard.

"I was at the front door and I was talking to my stepdad. I just started hearing these big pops," John Hedge told the station. "Pop, pop, pop. There was probably three or four, I hit the ground. I look up — the security guard is dead. Well, I don't want to say he was dead, but he was shot. He was down. The gunman was throwing smoke grenades all over the place. I saw him point to the back of the cash register ... and he just kept firing. I ran out the front door."

Panicked students and other patrons took shelter where they could, scrambling to hide from the gunman. Many fled when and how they could. One witness told NPR's Nate Rott that he and others were able to escape after they grabbed a bar stool and threw it through a back window.

When sheriff's deputies arrived at the scene, they were "still hearing shots" inside, said Capt. Garo Kuredjian of the Ventura County Sheriff's Office.

"The initial report indicated that a man had opened fire with a semi-automatic gun," the Ventura County Star reports, adding that "Officers on the scene indicated that approximately 30 shots had been fired and that victims would be at multiple locations as they fled."

Aerial footage from local news media showed a massive police response to the scene of the shooting, as multiple agencies sent officers to help.

Wednesday nights at the Borderline Bar & Grill are billed as Country College Night; Borderline's website advertises dance lessons at 9:30 and 10:30, and its Facebook page shows people line dancing.

In addition to Pepperdine, other colleges, including California State University, Channel Islands, and California Lutheran University are located a short drive from the bar.

Early Thursday, a family reunification center was set up down the highway from the Borderline; the sheriff's department says the site is also staffed with chaplains and the Red Cross.

The Ventura County Sheriff's Department says Helus' body will be taken from the hospital to the medical examiner's office today, in a procession scheduled for 10 a.m. local time.

"He leaves behind a wife and son," the agency said. Noting his heroic actions, it added, "Our hearts go out to his family and friends during this difficult time."

This is a breaking news story. As often happens in situations like these, some information reported early may turn out to be inaccurate. We'll move quickly to correct the record and we'll only point to the best information we have at the time.

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