The gunman who massacred 12 people at a country music bar in southern California on Wednesday night has been identified as an honorably discharged ex-Marine whose neighbors say he was plagued with PTSD and terrified his own mother.

Ian David Long, 28, opened fire on the Borderline Bar and Grill in Thousand Oaks at 11.20pm on Wednesday during its weekly College Country Night where students from nearby schools line dance and listen to music.