What to Know The shooting began about 11:15 p.m. at the Borderline Bar & Grill.

Twelve victims were killed, including a Ventura County Sheriff's sergeant. The gunman also died.

An emergency information hotline was set up for the #BorderLineShooting at 805-465-6650.

A gunman in a crowded Southern California bar sent people diving for cover and smashing windows to escape Wednesday night when he opened fire and killed 12 people, including a sheriff’s sergeant who responded to the call for help.

By early afternoon, 10 of the 12 victims had been identified.

One of the victims, 27-year-old Telemachus Orfanos, who had survived the Las Vegas Massacre, was slain amid the barrage of gunfire Wednesday night.

The gunfire began about 11:15 p.m. during College Country Night, a weekly event at the Borderline Bar & Grill. Hours later, parents and friends of those who remain unaccounted for were desperately searching for updates -- many in the crowd came from local colleges such as Pepperdine, Moorpark and Cal State Channel Islands.

The attacker, identified as a decorated 28-year-old Marine Corps veteran from the area, was found dead in an office at the bar after shooting himself, investigators said.

Ventura County Sheriff Geoff Dean said his agency received multiple calls of shots being fired at the bar, which has a large dance hall, pool room and eating and drinking area. About 150 to 200 people were inside at the time, Dean said.

"It's a horrific scene in there," Dean told a news conference in the parking lot of the bar.

Minutes after the first rounds were fired, sheriff's Sgt. Ron Helus, 54, and a California Highway Patrol officer went in to respond to the gunshots. Helus, a 29-year veteran looking forward to retirement soon, was speaking with his wife on the phone when he told her he needed to respond to an emergency.

"He went in to save lives," Dean said, his voice cracking. "He went in to save other people."

Helus was shot several times in an exchange of gunfire with the attacker, Dean said.

There were about six off-duty police officers inside the bar from several different agencies. Dean said it appears they took action to protect others and help them escape.

"I've already talked to a parent who came up and said, 'They stood in front of my daughter,'" said Dean.

Witnesses told The Associated Press the hooded gunman used a smoke bomb and was wearing all black with his face partly covered. He first fired on a person working at the door, then appeared to open fire at random.

The shooter was identified as 28-year-old Ian David Long, who served in the Marine Corps from August 2008 to March 2013 and was deployed to Afghanistan as a machine gunner in 2010. Deputies were searching his Thousand Oaks house early Thursday in connection with the shooting. Neighbors told NBC4 he lived at the home with his mother.

The weapon was a legally purchased Glock 21 .45-caliber handgun equipped with an extended magazine, Dean said. California has banned large-capacity magazines since 2000, though a law that would have extended the ban to magazines possessed before then has been tied up in the courts.

Dean added that the department has had "several contacts" with Long over the years. The most recent was in April when he was irate and acting irrationally, prompting a mental health crisis intervention team's involvement, Dean said. He was not taken into custody.

It is believed the gunman shot himself, he added. The body was found in an office next to the entrance.

There were no indications he specifically targeted anyone at the bar, Dean said.

Some witnesses reported breaking through windows and ducking under tables to escape the fusillade. Sarah Rose DeSon of Whittier, a communications major at Cal State Channel Islands in Camarillo, was celebrating a friend's birthday at the bar when she heard the gunfire and noticed what appeared to be a smoke bomb.

"All I remember was standing there with my friend and I heard the shots," she said. "I'm pretty sure I saw him. I'll never get that picture out of my head. We dropped, heard gunshots, a lot of gunshots.

"Everyone was under the table so it was hard to get under there. By the grace of God I got to the front door."

She ran down the stairs, got in a car, and circled the area, yelling her friend's name. She found her friend safe, hiding in the bushes.

A bomb squad was combing through the scene after some reported smoke bombs going off during the gunfire. There was no word on what motivated the shooting.

In the hours after the shooting, family members gathered a nearby unification center. After anxiously waiting all morning for word, Jason Coffman received confirmation that his 22-year-old son Cody was among the dead.

"I've been here fighting for him all morning long, and we did just get the news that he was one of the 11 killed last night," a devastated Coffman said. "He was Cody Coffman, my first-born son."

Family members confirmed the death of 18-year-old Alaina Housley, the niece of of actress Tamera Mowry-Housley. California Lutheran University said a 23-year-old recent graduate also was among the dead.

Recent graduate Justin Meek, 23, was killed in the shooting. The bar is just a few miles from the campus in Thousand Oaks.

The sister of Sean Adler also confirmed to NBC4 that her brother died in the shooting. He was working at the Borderline Bar on Wednesday nights to make extra money, she said.

Daniel Manrique, a veteran who was at Borderline Bar & Grill meeting other members of the military in support, was shot and killed.

The father of Telemachus Orfanos, known as Tel, said his son served in the Navy from 2011-2014. Tel, who loved to go to the popular Western-style bar and go line dancing, was among the several hundred people inside the venue around 11:15 p.m. He was shot and killed, his father told NBC4.

Mitchel Hunter, 19, from Simi Valley, said he saw the gunman. He said he had a short-barreled semi-automatic pistol with a big magazine.

He said he emptied the magazine and reloaded. The shooter was armed with a single handgun, according to a law enforcement source.

"I saw him walk in," Hunter said. "And he started shooting."

Hunter said his friend, Tim Munson, 19, also from Simi Valley, was hospitalized.

He didn't know his condition. Hunter said he heard some 20 shots and it seemed to take awhile before the police arrived.

"It took forever to get the cops there," he said.

Carl Edgar, a regular at the bar, said his mind was spiraling out of control.

"I'm grateful I wasn't there, but at the same time I wish I could've been there to help," Edgar said. "I don't have enough hands to count how many friends I have in there tonight.

"It's been a bad night. Wednesdays (are) the most popular because it's college night, just a bunch of lively kids, different colleges all the way from Ventura, all the way down to the Valley."

Edgar said his friends are OK.

The shooting came one day before Sheriff Dean planned to retire after 41 years of service. Bill Ayub will assume the post Saturday.

"Our thoughts and prayers go out to the victims and their families in the wake of this horrific tragedy. We are fully cooperating with local and federal law enforcement during their investigation. Please respect our privacy while we mourn the loss of so many lives," said the owner of the Borderline Bar, Brian Hynes.

The massacre was the deadliest mass shooting in the United States since 17 classmates and teachers were gunned down at a Parkland, Florida school nine months ago. It also came less than two weeks after a gunman killed 11 people at a synagogue in Pittsburgh. In May, 10 people were killed and 13 others injured when a gunman opened fire at Santa Fe High School in south Texas.

Beverly White, Jonathan Gonzalez, Robert Kovacik, Stephanie Marroquin and Oleevia Woo contributed to this report.