President Donald Trump has described the gunman responsible for killing 12 people in a California bar as “a very sick puppy”.
Investigators have not commented on a motive for the rampage or whether mental illness played a role.
But neighbours reported hearing frequent loud rows between Ian David Long and his mother, one of them so extreme they called police in April.
Authorities at the time worried that the 28-year-old Afghanistan war veteran might have post-traumatic stress disorder but a mental health specialist concluded there were no grounds to have him involuntarily committed.
On Wednesday night, the former machine gunner, dressed all in black with his hood pulled up, opened fire with a handgun at the Borderline Bar & Grill during college night, then apparently killed himself as scores of police officers closed in.
At the White House, Mr Trump touted his efforts to fund work on PTSD among veterans. He declined to engage on questions on whether the nation needs stricter gun control laws.
Julie Hanson, who lives next door to the ranch-style home that Long shared with his mother, described him as “odd” and “disrespectful” well before he left home a decade ago, got married and enlisted in the Marines.
She could often hear him yelling and cursing, but several months ago unusually loud banging and shouting prompted her husband to call authorities.
“I was concerned because I knew he had been in the military,” Tom Hanson said.
About 18 months ago, Don and Effie MacLeod heard “an awful argument” and what he believes was a gunshot from the Longs’ property. Don MacLeod said he did not call police but avoided speaking with Ian Long.
“I told my wife, ‘Just be polite to him. If he talks, just acknowledge him, don’t go into conversation with him,'” Don MacLeod said.
Thousand Oaks is a city of about 130,000 people about 40 miles from Los Angeles. It is annually listed as one of the safest cities in America.
- Press Association