The man who shot and killed at least 12 people in a mass shooting in Thousand Oaks, Calif., overnight has been identified. Associated Press reports that the shooter was 28-year-old Ian David Long.

According to multiple accounts, Long burst into a country bar called the Borderline Bar & Gill late Wednesday night (Nov. 7) and began firing on the hundreds of patrons who were there to attend a college country night. Authorities say he used a handgun, and so far no assault rifles have been found at the scene. Long was found dead at the scene, and his motive for the crime is under investigation.

According to ABC News, law enforcement swarmed a neighborhood in the Newbury Park area just before 7AM Thursday morning (Nov. 8) and roped off Long's house. One of Long's neighbors revealed he was a veteran, and that he suffered from PTSD.

"I don't know what he was doing with a gun," she said.

Other neighbors told ABC that Long lived at that house with his mother. ABC reports that the gun used in the attack was a .45-caliber handgun that was purchased legally.

CNN reports that Long used a Glock .45-caliber handgun, and Ventura County Sheriff Geoff Dean says he believes the shooter killed himself. The news outlet reports that Long was active in the U.S. Marine Corps from August 2008 to March 2013.

He'd had multiple previous run-ins with law enforcement, including an incident in April, when officers responded to a disturbance at Long's house and he was acting "irate and acting irrationally," according to Dean. After meeting with Long, a mental health specialist decided not to detain him.

12 people have been reported dead in the Thousand Oaks shooting, including Ventura County Sgt. Ron Helus, a 29-year veteran of law enforcement who intended to retire in a year. Helus is being remembered as a hero for trying to stop the shooting spree. Authorities say 10-12 others were injured in the shooting. No other names have yet been released.

Borderline's website lists John RichCollin RayeMark ChesnuttLee Brice and Tyler Farr among the artists who have performed there over the years, and Rich was among the country artists who responded to the tragedy on Twitter Thursday morning, along with Charlie Daniels, Morgan Wallen. LeAnn Rimes and Margo Price.

Country Stars React to the Mass Shooting in California

More From KGAB