Initial reports state the gunman drove a vehicle to the bar, walked up to the entrance and shot the security guard.
The carnage added Thousand Oaks to the seemingly endless list of American cities at which a mass shooting has occurred.
Colleagues of Helus describe him as a friend and an exceptional man and officer.
Helus had been with the Sheriff's Department for almost three decades, and planned to retire within the year, Ventura County Sheriff Geoff Dean said, holding back tears, during an early morning news conference Thursday.
"I went with 11 friends, so far we've only found six of them", Whittler said.
Long drove to the club, walked up to the entrance and gunned down an unarmed security guard standing outside, Dean said.
"We have called in our bomb team to go through and a couple of bomb dogs here that are checking the area", Dean said.
"We have not found any type of assault rifle inside the location", he said. The official said the 29-year-old man deployed a smoke device and used a.45-calibre handgun. He is survived by his wife and a son.
The gunman, now identified as 28-year-old Ian David Long of Newbury Park, was found dead after shooting patrons and law enforcement at Borderline Bar and Grill.
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.
Ventura County sheriff's spokesman Captain Garo Kuredjian said a procession was set for 10 a.m.to take Helus' body from Los Robles Hospital in Thousand Oaks to the examiner's office in Ventura.
Dean said the other prior encounters were a traffic accident and an incident in which Long was the victim of a battery at a bar.
President Donald Trump praised police for their "great bravery" in the California attack and ordered flags flown at half-staff in honor of the victims.
Here's what we know about the people who died in the shooting at the Borderline Bar & Grill in Thousand Oaks.
Also, both the Vegas and Borderline shootings involved country music.
The Borderline, which opened in the 1980s, calls itself "Ventura County's largest country dance hall and live music venue" with 2,500 square feet of wide-open dance floor, according to its website. Hundreds of people were estimated to have attended.
California State University, Northridge, said in a statement that Long was a student, last attending the university in 2016.
Investigators believe Long arrived Wednesday night at the bar in a auto, shot a security guard who was standing outside, and then stepped inside.
Some freshmen had planned an outing Wednesday to the bar, said Madeleine Carr, news editor at the Pepperdine Graphic, the student newspaper.