Long, 28, was a veteran in the Marine Corps and had previous encounters with local police, said Ventura County Sheriff Geoff Dean. He was found dead inside the Borderline Bar & Grill when a SWAT team and officers entered. Dean said Long may have killed himself, but that police were still investigating.
Long allegedly used a .45-caliber handgun, said Dean. Twelve people were killed during the attack at the bar, a popular hangout for students, in Thousand Oaks, Calif.
Police had not initially identified a motive and did not believe Long targeted any employees at the bar specifically.
Dean said his department had several previous contacts with Long, including a call to his home in April, when deputies found him acting irate and irrationally. The sheriff said a mental health crisis team was called at that time and concluded that Long did not need to be taken into custody.
The other prior encounters were a traffic accident and an incident when he was the victim of a battery at a different bar, Dean said.