Thousand Oaks, California, hosted a private ceremony for relatives of the 12 people who were killed in the shooting on Nov. 7, 2018.

Thousand Oaks, California, hosted a private ceremony for relatives of the 12 people who were killed in the shooting on Nov. 7, 2018.

Investigators say the officer who was killed, Sergeant Ron Helus, was accidently shot by another officer.

Twelve people were shot dead on Nov. 7 at a bar in Thousand Oaks, California.

Authorities described "chaos and confusion" at the Thousand Oaks, California, bar.

Sgt. Ron Helus was killed by a bullet fired from a California Highway Patrol officer's gun.

Twelve people were shot dead on Nov. 7 at a bar in Thousand Oaks, California.

Twelve people were shot dead on Nov. 7 at a bar in Thousand Oaks, California.

"Alaina was my little sister," she said about her niece.

Alaina was a victim in the Thousand Oaks shooting last week.

Sgt. Ron Helus was among the 12 people gunned down at the Borderline Bar in California.

Twelve people were killed in the Wednesday night shooting at a California bar.

The former Marine reportedly wrote, "I just thought ... life is boring so why not?"

A father's last words to his son killed in the mass shooting were "I love you."

The victims at the Borderline Bar and Grill during its "college night" event ranged in age from 18-54.

Authorities said preliminary information indicated the suspect appeared to be texting or posting during pauses in the rampage.

Ashton Kutcher is calling for more than thoughts and prayers in the wake of the mass shooting at a California bar.

Marine veteran may have had PTSD, Sheriff says

Telemachus Orfanos, 27, survived the Vegas shooting but died in Thousand Oaks.

The newly-obtained cellphone video captured six seconds of eerie silence after gunfire erupted at a bar in Thousand Oaks, California, killing 12 people.

Twelve people, including an officer who ran in to confront the gunman, were killed after the shooter opened fire at the Borderline Bar and Grill on Wednesday night.

The mother of Telemachus Orfanos said, "I hope to God nobody else sends me any more prayers."

"It's difficult, because I've been doing this for 41 years, and you don't leave things unfinished," Ventura County Sheriff Geoff Dean, who'd been considering retirement, told ABC News' David Muir.

The country-themed Borderline Bar and Grill was packed at the time.

Ian David Long, a former machine gunner and Afghanistan war veteran killed 12 people at a country western bar in an attack, officials said.

Ventura County Sgt. Ron Helus, a 29-year veteran, was killed in the line of duty when he heroically entered the building and confronted the gunman.

ABC News have learned the names of some of the dead and the details of their unfinished lives.

28-year-old Ian David Long, had a legally purchased .45 caliber handgun and was found dead inside the Borderline Bar & Grill after the overnight shooting, authorities said.

She had been in contact all morning with her roommate looking for answers.

The shooter in a mass killing was a white man wielding a handgun, sources said.

At least one of the survivors of Thousand Oakes’s night club shooting was also a survivor at Las Vegas music concert shooting last year.

A video posted to Instagram shows the inside of Borderline Bar and Grill as shots are being fired.

"Borderline was our safe space," said Brendan Kelly, who also survived the mass shooting in Las Vegas last year.

"My life is changed forever," Jason Coffman said of the death of his son, Cody.

"I was lucky enough to get out alive," one witness said. "It does not feel real. I'm in shock, I'm in shock. I'm terrified."

Survivors of the mass shooting in Thousand Oaks, CA, speak about what happened when a gunman fatally shot 12 people.

The alleged gunman in the mass shooting in Thousand Oaks is also dead.

Police have identified the suspect in the Thousand Oaks shooting as Ian David Long.

Teylor Whittler, Sarah Rose DeSon and Nellie Wong were celebrating a 21st birthday at the Borderline Bar and Grill when the gunman burst in and opened fire.

FBI and other law enforcement officials scoured the suspected shooter's house.

The 19-year-old called her father and told him she was hiding near cactus.

President Trump has ordered flags to be lowered at half-staff until sunset on Nov. 10 as a mark of "solemn respect for the victims."

ABC News' Kanya Whitworth reports from Thousand Oaks, California, where 12 people were killed at a bar.

Hundreds of students were gathered for college night at the Borderline Bar and Grill in Thousand Oaks, California, when a gunman burst in.

Sgt. Ron Helus, a 29-year veteran of the Ventura County Sheriff's Office who was about to retire, is survived by his wife and his son.

There were hundreds packed inside Borderline Bar and Grill in Thousand Oaks, California, Wednesday night when a gunman burst inside.

Ian David Long allegedly killed 12 people in a bar in California.

When the shooting broke out, bar patrons courageously helped others.

The shooter in a killing rampage at a bar in Thousand Oaks, California, has been identified as David Ian Long, multiple law enforcement officials told ABC News.

Tim Dominguez was at the Thousand Oaks, California, bar with his stepson when the young victims were "out having a great time" before being shot.