The shooter has been identified as 28-year-old Ian David Long, who also died in the attack.
Authorities said Long was found dead at the scene after he had killed12 people, including a sheriff's deputy, and was confronted by officers who had stormed the bar. Dean told the Los Angeles Times that the amount of blood within the vicinity made it hard to determine whether Long killed himself or was shot to death by police.
Authorities haven't determined a motive.
Sheriff's Capt. Garo Kuredjian said investigators were still interviewing witnesses, have served a search warrant at Long's home and searched the vehicle Long drove to the bar. "It's particularly ironic that after surviving the worst mass shooting in modern history, he went on to be killed in his hometown", his father told the Ventura County Star.
He said the death toll may have been even higher were it not for Sgt Helus' bravery.
Authorities described an attack of military efficiency.
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Helus was the first officer to confront Long before Long eventually killed himself. All of the injured suffered cuts, bruises and other minor injuries in frantic attempts to escape the gunfire.
He said he and others smashed their way out of the bar onto a balcony and then jumped down to safety.
The Ventura County Sheriff's office requested that the social media service preserve the communications until the posts can be subpoenaed with a search warrant or court order.
A few weeks after the Vegas shooting, the bar held a benefit concert for five people from the area who were killed, and now-eerie social media posts show a number of survivors holding up a "Route 91" sign inside the bar at a six-month anniversary event.
The official was briefed on the investigation into Wednesday's night shooting but wasn't authorized to discuss it publicly and spoke to the AP only on condition of anonymity.
Long grew up in Thousand Oaks and several people who knew him described him in disturbing terms.
Long made others feel uncomfortable going back to his teens.
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"There are hundreds of thousands of people with PTSD", said Dominique Colell, a track coach at Newbury Park High School, which Long attended.
"(He) said to her, 'Hey I got to go handle a call.
"Ian came up and started screaming at me that was his phone", Colell said. "He was the only athlete that I was scared of".
Colell said she wanted to kick Long off the team, but the boy's coach urged her to reconsider because that could compromise his goal of joining the Marines. At the White House on Friday, Trump touted his efforts to fund work on post-traumatic stress disorder among veterans and ignored questions about stricter gun control laws.
"He didn't come home last night", Schmidt-Orfanos said. "I suspected he had a gun there because I heard a gunshot one night, over a year ago".
Neighbours reported hearing frequent loud rows between Long and his mother, one of them so extreme they called police in April.
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