Ventura Sheriff's Sergeant Ron Helus, who later died in hospital, had tried to enter the active scene with a local highway patrolman when he was shot several times.
"Sgt. Helus will be transported via motorcade from Los Robles Hospital to westbound Janss Road", the department said in a statement.
Tom Hanson, 70, who lives next door to Long and his mother, said Thursday that he called the police about six months ago when he heard "heavy-duty banging" and shouting coming from the Longs' home.
Dean says around 10 other people were shot and wounded.
A Ventura County Sheriff's Office official said approximately 30 shots had been fired inside the building.
"He was hard-working, he was totally committed, he gave his all and, tonight, as I told his wife, he died a hero", Dean said at a press conference early Wednesday. "Our hearts go out to his family and friends during this hard time", the department added. "I love you. I'll talk to you later, "' Dean said. Eyewitnesses said people used chairs to break the windows and escape.
At least 12 others, including the killer, were killed during the attack, and 15 others were injured during the incident, which occurred during "College Country" night. "He's taken many young lives".
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He said he has no doubt Helus' tactics at the scene "were sound when he went in". "I just started hearing these big pops. You know, I think it's going to be something that we're going to have to come together and move past".
Some people who were inside the bar said they had survived the deadly mass shooting at the Route 91 Festival in Las Vegas past year.
He said first responders arrived just three minutes after the first emergency calls from the venue were made.
Another witness said there was numerous shots fired inside the bar. My son thought it was a joke, so I pulled him down and got some cover.
A neighbour, who would only identify himself by his last name, Mr Hanson, said Long lived with his mother.
Tayler Whitler, 19, said she was on the dance floor when she saw the gunman shooting and heard screams of "Get down!"
"It was really, really really shocking", Whitler told KABC-TV as she stood with her father in the Borderline parking lot.
People hugged after praying before the procession carrying the body of Ventura County Sheriffs Sgt. Ron Helus.