A Ventury County sheriff's sergeant killed in the shooting last month at Borderline Bar and Grill was shot five times by the gunman, but it was a sixth bullet from a California Highway Patrol officer that claimed his life, authorities said Friday.

Shortly after the gunman opened fire inside the Thousand Oaks bar on Nov. 7, Sgt. Ron Helus answered a call for help and rushed inside.

At a news conference Friday, Ventura County Sheriff Bill Ayub said Helus died from a bullet fired by a CHP officer that struck vital organs.

"This was a dynamic, chaotic event that led to a very brief but furious gun battle between the killer and the lawmen," Ayub said. "We believe that Sgt. Helus was clearly not the intended target of the CHP officer -- which further illustrates the extreme situation both men faced."

12 people lost their lives in the shooting

Investigators have previously said they don’t know why 28-year-old Ian David Long stormed into the bar and opened fire as people were dancing to country music.

The former Marine killed 12 people, including Sgt. Helus, before taking his own life.

Helus, 54, was on the SWAT team for much of his career and worked in narcotics and investigations. He was a 29-year veteran of the sheriff's department.

Gov. Jerry Brown and members of the law enforcement community from around the nation attended Helus' funeral on Nov. 15. 

The Associated Press contributed to this report.