Hundreds of people were inside the Borderline Bar & Grill in Thousand Oaks when Long, armed with an uzi, unleashed a terrifying barrage of smoke bombs before opening fire and killing 12 people, leaving "blood everywhere".
Authorities believe Ian David Long eventually turned the gun on himself, but not before the 28-year-old, dressed in all black, terrorized a crowd filled with college students at Borderline Bar & Grill in Thousand Oaks, Calif.
Ventura County Sheriff Geoff Dean told reporters one of the first officers to arrive at the Borderline Bar & Grill in the city of Thousand Oaks was shot after going inside the confront the shooter.
He died at a hospital.
A "dedicated" police officer who was one year from retirement died in the California bar massacre while trying to stop the gunman, it emerged today. "He went in there to save people and made the ultimate sacrifice", said Dean. No other information on them was immediately known.
Dean said around 10 other people were shot and wounded.
It was "College Country Night" and two-step lessons were being offered Wednesday at the Borderline, according to its website.
It was the deadliest mass shooting in the USA since 17 students and teachers were killed at a Parkland, Florida, high school nine months ago.
It was the second mass shooting in America in less than two weeks. They found Long "somewhat irate, acting a little irrationally", Dean said.
Numerous patrons were local students from nearby California Lutheran University, ages 19 to 25, attending "College Country Night".
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The sheriff of Ventura County, California is describing what happened late Wednesday night when a gunman killed 12 people at a bar.
A witness told KABC-TV that there were many young people "having a great time" in the bar when a man entered and "started shooting".
The Los Angeles Times quoted a law enforcement official as saying at least 30 shots had been fired.
"Sergeant Helus served with the Ventura County Sheriff's Office for 29 years and is survived by his wife and son". "I love you. I'll talk to you later".
Dean said Long was a veteran of the United States marine corps.
Video accessed by the AP showed law enforcement officers and vehicles speeding to the scene and people running from the bar.
Dean confirmed the weapon was purchased legally, a.45 caliber Glock 21 handgun. "Get out! Let's go!'" she added.
"As soon as he walked in he had flawless form", said Whittler, who added she grew up in a military family.
The shooting began at 23:20 local time on Wednesday about 40 miles (65km) north-west of Los Angeles, police say.
Mitchell Hunter says the shooter was wearing a trench coat and shooting a handgun with a long magazine.