Thousand Oaks, CA – Ventura County Sheriff Bill Ayub has announced that one of the six rounds that hit Sergeant Ron Helus during the mass shooting at the Borderline Bar & Grill on Nov. 7 was fired by a fellow officer.

Ian David Long, 28, fired the other five rounds which struck the sergeant and killed 11 other people inside the packed country-music bar before he turned the gun on himself, USA Today reported.

“This was a dynamic, chaotic event that led to a very brief, but furious gun battle between the killer and the lawmen, Sheriff Ayub said during a press conference on Friday.

“Today, I’m deeply saddened to inform you that Sgt. Helus was also struck by a sixth bullet, which we now know, through forensic analysis by the FBI’s crime laboratory, was fired from the CHP officer’s rifle,” he explained. “Tragically, it struck vital organ and was fatal.”

The bullet struck Sgt. Helus in the heart, police said.

The California Highway Patrol officer who fired the round is a nine-year veteran of the department with prior military experience, USA Today reported.

He has been on personal leave since Wednesday, when he was told that the bullet that killed Sgt. Helus came from his weapon.

“The California Highway Patrol…is profoundly saddened to learn of new details emerging from the horrific incident which resulted from the deadly actions of suspect Ian David Long at the Borderline Bar on Nov. 7,” California Highway Patrol Commissioner Warren Stanley said in a statement on Friday, according to USA Today.

“The suspect, who had been lying in wait for the officers to arrive, immediately ambushed the pair with gunfire as they entered the building,” Commissioner Stanley said. “While the officers’ actions prevented the suspect from shooting more patrons, tragically, during the brief and chaotic gunfight that ensued, a round by our officer struck Sgt. Helus.”

Commissioner Stanley extended his condolences to the family, friends and colleagues of the fallen hero.

“Without question, Sgt. Helus died a hero while protecting his community from a dangerous criminal,” he continued. “In the face of danger, Sgt. Helus courageously upheld the oath he took to lay down his life rather than swerve from the path of duty.”

Investigators have yet to determine a motive for Long’s attack, which occurred at approximately 11:20 p.m. as hundreds of patrons were enjoying a university student night inside the bar, BBC reported.

Armed with a .45-caliber Glock pistol, the hooded gunman first shot the security guard outside, according to NBC News.

He then tossed smoke bombs into the crowd, “turned to the right, shot several other security and employees and began opening fire inside the nightclub,” Ventura County then-Sheriff Geoff Dean said at the time.

Long fired over 50 rounds during the mayhem.

According to witnesses, patrons inside the bar mostly fell silent and fled to various corners of the building, attempting to hide, CNN reported.

“He didn’t say anything, at least not that we could hear, witness Matthew Estron told NBC News. “Everyone was just trying to get out.”

Others tossed stools through windows and hoisted people out, saving dozens of lives, CNN reported.

“It’s too bad I won’t get to see all the illogical and pathetic reasons people will put in my mouth as to why I did it,” Long wrote in a social media post he made during the attack, according to TMZ. “Fact is I had no reason to do it, and I just thought…f–k it, life is boring so why not?”

“I hope people call me insane…wouldn’t that just be a big ball of irony?” the gunman wrote. “Yeah…I’m insane, but the only thing you people do after these shootings is ‘hopes and prayers’ .. or ‘keep you in my thoughts’ … every time … and wonder why these keep happening …”

Sgt. Helus, a 29-year veteran of the force, was among the first law enforcement officers to respond to the scene, Sheriff Dean said told CBS News at the time.

“When he heard gunfire, he went in and that’s something [we] would expect from Ron,” he said, according to KCBS.

“He was willing to sacrifice his life for the sake of others,” the sheriff noted, according to NBC News. “He ran into danger — he didn’t walk.”

He was shot multiple times after he entered the building, and was later pulled to safety by a California Highway Patrol trooper, CBS News reported.

Sgt. Helus, 54, was rushed to a local hospital, where he died at approximately 2 a.m. on Nov. 8.

The gunman murdered 11 other people during the attack, and wounded 10 to 15 more, Sheriff Dean said, according to CNN.

Long was later found dead inside the bar.

“When the officers made entry, the suspect was already deceased,” Sheriff Dean said during the press conference. “There are 11 victims. I will not count the suspect as a victim.”

“This is, by far, the most horrific thing I’ve seen in my 41 years,” he told NBC News.

The sheriff described Sgt. Helus as a “hardworking, dedicated” public servant, CBS News reported.

“It’s so tragic losing Ron,” Sheriff Dean said, according to CNN. “We go to the gym together, work out together. It’s horrific and terrible and it saddens our hearts.”

The married father-of-one had given nearly three decades of his life to his department, and planned to retire in about a year.

“He went in to save lives, to save other people,” Sheriff Dean said at the time. “He was totally committed, he gave his all, and tonight, as I told his wife, he died a hero.”