THOUSAND OAKS (CBSLA) — A Marine was identified as the shooter who killed 12 people, including a Ventura County sheriff’s sergeant, at a Thousand Oaks bar before apparently killing himself.

Ian David Long, 28, had several contacts with the Ventura County Sheriff’s Department over the years, ranging from minor incidents like traffic citations and collisions, to being a victim of battery at a local bar in January of 2015, Sheriff Geoff Dean said.

READ MORE: Firefighters Extinguish Fire That Started In The Walls, Spread To Ceiling Of Buena Park Strip Mall

The bar where Long was battered was not the Borderline Bar & Grill, where authorities say he gunned down patrons attending a “college country night” before apparently shooting himself.

The shooting, reported at about 11:20 p.m., left 12 dead, including Ventura County sheriff’s Sgt. Ron Helus, a 29-year veteran of the department.

More recently, sheriff’s deputies made contact with Long in April of this year, when they were called to his home on a report of “subject disturbing.”

“He was irate, acting a little irrationally,” Dean said, so deputies who responded to the incident called out the department’s crisis intervention team, who met with him and cleared him.

READ MORE: With California's Reopening, Father's Day Celebrations Regain Some Sense Of Normalcy Across The Southland

“They didn’t feel he was qualified he needed to be taken under 5150,” Dean said, referring to a mental health hold.

Dean confirmed Long was a Marine Corps. corporal. He served between August 2008 and March 2013 and served as a machine gunner. He had been deployed to Afghanistan between 2010 and 2011, and his last duty assignment was in Hawaii.

The sheriff said Long may have been suffering from PTSD. Long was also a student at Cal State Northridge.

The gun used in Wednesday’s shooting was purchased legally and identified as a Glock 21 45-caliber handgun that had an extended magazine. Dean said the weapon is still being processed and it’s not clear how many rounds were on it.

MORE NEWS: Fiery Fatal Car Crash In Irvine Kills One Victim, Identified As 20-Year-Old Nicholas Beamon

Investigators still have no motive for the shooting.