Ventura County Sheriff Geoff Dean addresses the media Nov. 8 after a mass shooting in Thousand Oaks. Photo by Tony Biasotti.

Updated at 12:30 p.m. Nov. 9:

A Marine combat veteran killed 12 people and himself late Nov. 7 after he opened fire at The Borderline Bar and Grill, a country music bar in Thousand Oaks, authorities said Thursday.

Hundreds of people fled in panic and dozens were injured before the killer, identified as 28-year-old Ian David Long, a former machine gunner and veteran of the war in Afghanistan, took his own life after a shootout with law enforcement.

The dead included 11 people inside the bar and a veteran sheriff’s sergeant who was the first officer inside the door, Ventura County Sheriff Geoff Dean said.

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

Helus was immediately hit with multiple gunshots, Dean said. The highway patrolman pulled Helus out, then waited as a SWAT team and scores more officers arrived. Helus died early Nov. 8.

By the time officers entered the bar again, the gunfire had stopped, according to the sheriff. They found 12 people dead inside, including the gunman, who was discovered in office and had apparently shot himself, the sheriff said.

“There’s no doubt that they saved lives by going in there and engaging with the suspect,” said Dean, who was set to retire on Nov. 9. “He went in there to save people and paid the ultimate price.”

Highway 101 northbound was expected to be shut down the morning of Nov. 8 as a procession carried the body of the slain officer to the Ventura County Medical Center.

In addition to the dead, at least one other person was wounded by gunfire, and as many as 15 others suffered minor injuries from jumping out windows or diving under tables, authorities said.

Los Robles Regional Medical Center treated and released 10 victims of the shooting for gunshot and laceration wounds.

“On behalf of the care team of Los Robles Regional Medical Center, we extend our sympathies and thoughts of support to the victims and their family members as we face this tragic aftermath,” the medical center said in a Nov. 8 news release. Treatment for victims of the shooting began just after midnight on Nov. 8. The trauma center and ER teams, along with supporting departments, worked to triage and treat victims.

People at the bar, a popular hangout for students from nearby California Lutheran University, fled from all exits, broke through windows and hid in the attic and bathrooms, the sheriff said.

Among the fatalities was 23-year-old Justin Meek, a CLU student and bouncer at the Borderline; 18-year-old Alaina Housley, a freshman at Pepperdine University; and 22-year-old Cody Coffman.

CLU cancelled classes Nov. 9 because of nearby wildfires but still offered counseling and ministry services to students still on campus. A vigil planned for 4 p.m. Nov. 9 was postponed.

The Center for Economic Research and Forecasting’s annual Ventura County forecast presentation slated for Nov. 8 was also cancelled.

Pepperdine  said 16 Pepperdine students were in the bar at the time of the incident. One of those students remains unaccounted for and two students were treated and released from the hospital.

A family assistance center was set up at the Thousand Oaks Teen Center at 1375 E. Janss Road and the sheriff’s department posted an information hotline at (805) 465-6650.

Congressman Salud Carbajal said he had formerly taught a program at the campus and was devastated to hear that students were involved.

“I am incredibly grateful to Sheriff’s Deputy Ron Helus, who exhibited instinctual bravery and sacrifice during this dangerous shooting and ultimately lost his life,” he said in a statement Nov. 8. “Thank you to all of the law enforcement officers at the scene who put their lives on the line for their community.”

Carbajal added a call for firearm reforms, saying that the event was part of a gun violence crisis.

“This shooting comes just eleven days after the last mass shooting in our country,” he said, referring to a gunman who killed 11 people at a synagogue in Pittsburgh. “Congress must act now to pass meaningful reforms to save lives and prevent future tragedies.”

Long was armed with a Glock 21, a .45-caliber 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.

Authorities searched Long’s home in Newbury Park, about 5 miles from the Borderline bar.

“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.”

The Marine Corps said Long served from 2008 to 2013, rose to the rank of corporal and was sent to Afghanistan in 2010-11, receiving several medals and commendations.

Authorities said he had no criminal record, but Dean said officers were called to his home in April, when 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.

A Conejo Valley Victims Fund for victims and their families has been set up by the Ventura County Community Foundation, in coordination with the city of Thousand Oaks, California Community Foundation, Conrad N. Hilton Foundation, Amgen Foundation and others. Donations can be made at https://vccf.org/donate/make-a-donation/

Although a few GoFundMe and other donation pages have popped up online, a spokeswoman for the city of Thousand Oaks directed people to donate to the VCCF’s campaign, which she said is the only campaign vetted and verified by the city. Victims and their families will receive 100 percent of the proceeds from this fund, she said, with no middleman fees charged by the foundation.

If you donated to a GoFundMe campaign you believe to be suspicious or fake, you can fill out a claim form at www.gofundme.com/guarantee and report the account on the GoFundMe website.

Other community fundraising efforts include the Ventura Harbor Comedy Club’s Nov. 8 event, which turned into a benefit for the Conejo Valley Victims Fund with a special appearance from Vietnam Veteran Blake Clark from “50 First Dates” and “Toy Story 4,” according to a Twitter post from the club.

A blood drives for victims will be held from 1-7 p.m. Nov. 9 at the Santa Susana Community Center in Simi Valley.

• Staff writers Marissa Nall and Annabelle Blair and The Associated Press contributed to this report.