But neighbors reported hearing frequent loud fights between Ian David Long and his mother, one of them so extreme they called police in April, and authorities at the time anxious that the 28-year-old Afghanistan war veteran might have post-traumatic stress disorder, though a mental health specialist concluded there were no grounds to have him involuntarily committed. He also used a smoke bomb, said an official.
Neighbours said they had heard frequent loud fights with his mother and that police were called out in April - though on that occasion mental health experts decided intervention was not needed. Instead, when Long shot, he killed.
"We have no idea what the motive was at this time", Dean said, adding that Long was veteran who had served in the Marine Corps.
Among the 12 victims are Ventura County Sheriff's Deputy Ron Helus, a 29-year veteran of the force who was the first to arrive on the scene, as well as actress Tamera Mowry-Housley's niece, 18-year-old Pepperdine student Alaina Housley.
Mourners outside a reception centre for families of victims.
The bloodshed was the latest in what seems to be a never-ending string of mass shootings that are happening with terrifying frequency across the United States.
The shooting in Thousand Oaks took place just 11 days after another gunman - identified as Robert Gregory Bowers - carried out an attack on the Tree of Life synagogue in Pittsburgh, killing 11 people.
President Donald Trump was briefed on the shooting and praised law enforcement officers for their response.
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Julie Hanson, who lives next door to Long's ranch-style home, described him as "odd" and "disrespectful" well before he left home a decade ago, got married and enlisted in the Marines, becoming a machine-gunner.
Mr Coaly said that his friend is in good condition and with his dad. When the shooter reloaded, he got his friends out.
Helus and a highway patrol officer exchanged gunfire with Long, he said, and the sergeant was shot "several times".
He said Helus was on the SWAT team for much of his career and worked in narcotics and investigations. He was shot inside and later died at a hospital.
Telemachus Orfanos was a graduate of Thousand Oaks High School and later joined the Navy, according to his Facebook page.
"Ron was a hardworking, dedicated sheriff's sergeant who was totally committed", Dean said, choking back a few tears and clearing his throat.
Alexis Tait, 23, said she heard what sounded like firecrackers going off until she saw her friend Kristina Kaylee Morisette fall to the floor - one of a dozen people the gunman killed.
"He went in there to save people and paid the ultimate price", he said. Thousands of people stood along the route.