NEWBURY PARK, Calif. — The authorities on Thursday identified Ian David Long, 28, as the gunman in the mass shooting at the Borderline Bar & Grill in Thousand Oaks, Calif.
The Ventura County Sheriff’s Office said Mr. Long, of Newbury Park, Calif., killed 12 people in an attack late Wednesday night on the bar, which was crowded with people dancing to country music. He appeared to have died from a self-inflicted gunshot wound after exchanging fire with officers at the scene, the authorities said.
Here is what we know about the gunman:
• Sheriff Geoff Dean said deputies had several interactions with Mr. Long in recent years. One of the encounters involved a reported disturbance at his home in April that prompted mental health specialists to talk to him.
• The specialists who spoke with Mr. Long discussed his service in the United States Marine Corps and whether he had suffered from post-traumatic stress disorder. They determined that he was not an immediate danger to himself or others and that he could not be involuntarily taken to a mental hospital.
• Sheriff Dean said that Mr. Long was the victim in a January 2015 fight at a different bar in Thousand Oaks.
• Mr. Long had served in the Marine Corps from August 2008 to March 2013, including a seven-month deployment to Afghanistan that began in 2010, according to military records. He served as a machine gunner and obtained the rank of corporal.
• After the Wednesday night shooting, the authorities recovered a handgun inside the Borderline Bar & Grill, a Glock 21 .45-caliber handgun, which they believe Mr. Long used in the attack. The firearm had been outfitted with an extended magazine to hold more bullets than a typical handgun. It had been purchased legally, Sheriff Dean said.
• Mr. Long first shot a security guard outside the bar, went inside and then shot more employees before opening fire on patrons.
A neighbor says he called the police this spring over shouting coming from Mr. Long’s home
The police and F.B.I. agents arrived at the neatly kept suburban home where Mr. Long lived with his mother just after 7 a.m. on Thursday.
Tom Hanson, 70, who has lived in the home next to the Longs for decades, said that Mr. Long and his mother moved in when Mr. Long was in middle school. He said that after Mr. Long returned from his military service, he rarely left the home.
Mr. Hanson also described hearing shouting coming from the home several times one morning this spring. He became concerned, he said, and called 911.
“I didn’t know if he was going to kill himself or what he would do, so I called the sheriff to investigate,” he said.
“He rarely spoke to me, but that didn’t bother me,” he added. “People have their own lives, we’re different ages, different concerns.”
Mr. Hanson said he had countless friends who were Vietnam veterans with whom he used to get together for casual basketball or football games. He motioned to the street in front of his home, now cordoned off with red crime scene tape.
“We’d spend time together, get air, blow off some steam,” Mr. Hanson said. “It’s not like that now, this guy just kept to himself, probably tried to deal with whatever he had on his own.”
Jennifer Medina reported from Newbury Park, Calif., and Serge F. Kovaleski and Matthew Haag from New York. Kitty Bennett contributed research.