WARNING: Graphic — Gunshots & Yelling Inside California Country Music Bar Massacre

Chilling video from inside a California country music bar reveals the moment a crazed mass shooter opened fire Wednesday night, eventually killing 12 people, including a sheriff's sergeant.

In video obtained by RadarOnline.com and posted to Instagram by a man identified as Dallas Knapp, who was inside the Borderline bar when 28-year-old Ian David Long, shows the former machine gunner and veteran of the war in Afghanistan shooting.

In the horrifying clip, you can hear Long load up a second round of bullets and shooting victims on the ground who were already wounded.

“I looked him in his eyes while he killed my friends I hope he rots in hell for eternity,” Knapp commented. “The guy you see is the murderer and the shots are him shooting the wounded on the ground.”

As RadarOnline.com has been reporting, the dead included 11 people inside the bar and a veteran sheriff’s sergeant who was the first officer inside the door.

Among those killed was Alaina Housley, niece of The Real host Tamera Mowry.

“Our hearts are broken. We just learned that our niece Alaina was one of the victims of last night’s shooting at Borderline bar in Thousand Oaks,” Mowry and her husband Adam Housley revealed in a statement to US Weekly.

No motive is known yet for the massacre, but Long does have a history with police, who just months earlier were called to his home in Newbury Park following a disturbance, RadarOnline.com can confirm.

The military veteran had been acting erratically, and concerned neighbors called cops.

“We received a call for a disturbance, so we went out there and contacted him,” Ventura County Sheriff Geoff Dean told RadarOnline.com. “He was quite distressed, so we called our mental heath professionals, which is our crisis intervention team.

“They evaluated him and decided he did not qualify under 5150 to be taken in. They gave him some referrals, talked to him for a while and released him. We then left the area.”