Elliot Rodger’s parents tried to stop him after receiving an email minutes before killing six people in Santa Barbara on Friday, says a family friend.
They raced to Isla Vista but heard radio reports on the shootings as they drove, friend Simon Astaire told US media.
Elliot Rodger, 22, warned of his intentions in his emailed manifesto and a YouTube video posted the day before.
Hundreds gathered at a memorial service in the college town to mourn the dead.
Three more of the victims were named on Sunday night – Cheng Yuan Hong, 20, George Chen, 19, and Weihan Wang, 20, were stabbed in Elliot Rodger’s apartment.
They were his first victims before he killed three more and wounded 13 others in a shooting rampage.
Elliot Rodger died after speeding through the town in his black BMW, exchanging fire with police, authorities said.
He was found dead in his car from a gunshot wound to the head, believed to be self-inflicted, with three legally purchased semi-automatic weapons.
Moments before he began opening fire, Elliot Rodger emailed his parents, therapist and others to inform them of his intentions in a 140-page “manifesto” entitled Day of Retribution.
Elliot Rodger’s mother Li Chin called the police before she and ex-husband Peter Rodger raced to Isla Vista from Los Angeles in separate cars, but heard en route about the shooting, family friend Simon Astaire told US media.
In a video posted on YouTube on Thursday, Elliot Rodger spoke of his plan to “slaughter” women at a sorority house at the University of California at Santa Barbara.
He described the rejection he felt because he had never been able to attract girls, and how he intended to exact revenge.
Santa Barbara County Sheriff Bill Brown said his department had visited Elliot Rodger at the end of April at the request of his family when they saw disturbing videos he recorded but officers found him to be polite and courteous, and no further action was taken.
Elliot Rodger had seen therapists off and on since he was nine years old and possessed “an underlying sadness”, Simon Astaire told Reuters. There was no suggestion he had any interest in guns.
In his manifesto, he said he feared police would foil his plot when they visited him.
“I had the striking and devastating fear that someone had somehow discovered what I was planning to do, and reported me for it,” Elliot Rodger wrote.
“If that was the case, the police would have searched my room, found all of my guns and weapons, along with my writings about what I plan to do with them.
“I would have been thrown in jail, denied of the chance to exact revenge on my enemies. I can’t imagine a hell darker than that.”
Katherine Cooper, 22, Veronika Weiss, 19, and Christopher Martinez, 20, were earlier named as Elliot Rodger’s shootings victims.
In an emotional statement, Ricardo Martinez said the death of his son Christopher had left his family “lost and broken”, and he blamed “craven politicians” and gun rights advocates.
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