Long opened fire, seemingly at random, inside the barn-style, Western-themed bar at about 11:30 p.m. PST (0730 GMT Thursday), using a .45 caliber Glock handgun equipped with a high-capacity magazine, Ventura County Sheriff Geoff Dean said.
Long was in the Marine Corps from 2008 to 2013, reaching the rank of corporal and serving as a machine gunner in Afghanistan, and the sheriff said he may have suffered from post-traumatic stress disorder.
“Obviously, he had something going on in his head that would cause him to do something like this,” Dean said.
Dean told reporters that in April officers had gone to Long’s home in nearby Newbury Park, about 4 miles (6 km) from the bar to answer a disturbance call and found him agitated. Mental health specialists talked with Long and determined that no further action was necessary, the sheriff said.
“He was raving hell in the house, you know, kicking holes in the walls and stuff and one of the neighbors was concerned and called the police,” Richard Berge, who lived one block away from the home, told Reuters. “They couldn’t get him to come out, so it was like a standoff for four or five hours.”
Berge, who took care of Long’s mother’s dogs, said she told him following that incident she worried her son might take his own life but did not fear he would hurt her.
Dean said he had been told that 150 to 200 people were in the Borderline at the time Long opened fire, adding: “It could have been much, much worse.”
Asked what the scene inside the bar was like, Dean said, “Like … hell.” Earlier he had described it as “a horrific scene in there. There is blood everywhere and the suspect is part of that.”
The Ventura County Sheriff’s Department said 21 people had been treated for injuries and released at area hospitals.
LATEST MASS SHOOTING
The massacre was the latest shooting rampage in the United States amid a fierce debate over gun control.
After a man fatally shot 11 worshipers at a Pittsburgh synagogue last month, U.S. President Donald Trump said their deaths could have been prevented if an armed guard had been stationed inside the temple.
Long shot an unarmed security guard outside the bar before going inside, where he fired on security staff, CNN reported.