ROUGH CUT (NO REPORTER NARRATION) A U.S. Marine Corps veteran opened fire on a crowd of mostly college students and young adults dancing at a crowded country and western bar in a suburb of Los Angeles late on Wednesday, killing 12 people including a sheriff's deputy.

The gunman, identified by authorities as Ian David Long, 28, was also found dead on Wednesday night in the office of the Borderline Bar and Grill, located in Thousand Oaks, a suburb about 40 miles from Los Angeles, apparently having shot himself.

Ventura County Sheriff Geoff Dean told a news conference on Thursday morning that Long was a Marine Corps veteran and had apparently fired at random with a .45-caliber Glock handgun with an extra-capacity magazine.

There was no known motive.

"Obviously he had something going on in his head that would cause him to do something like this," Dean said.

"Obviously he had some sort of issues." He said authorities were obtaining a search warrant for Long's home.

The Borderline is popular with university students and on Wednesday night was hosting College Country Night.

California Lutheran University, located about 5 miles from the bar, canceled Thursday's classes while Pepperdine University, about 20 miles away, planned a prayer service.

One of the victims was Sheriff's Sergeant Ron Helus, a 29-year veteran of the department who died at a hospital, Dean said.

Helus and a California Highway Patrol officer were the first to arrive at the bar and went inside just before 11:30 p.m.

PST (0730 GMT).

A statement from the sheriff's office said there would be a procession in honor of Helus, who leaves behind a wife and son, on Thursday morning.

"Ron's selfless, heroic actions will never be forgotten," the statement read.