A 22-year-old man who killed six people in a violent rampage in California convinced police he wasn’t a threat to others in a meeting prior to the attack, officials say.

Santa Barbara County Sheriff Bill Brown said on Sunday authorities had received a tip on April 30 concerning Elliot Rodger, who took his own life after Friday’s killing spree in the town of Isla Vista, outside the University of California at Santa Barbara.

A local mental health department official requested law enforcement carry out a welfare check on Rodger following the tip-off, and sheriff’s deputies visited the troubled man, Brown told CNN.

“They found him to be rather shy and timid, polite, well-spoken,” Brown said.

“He explained to deputies that it was a misunderstanding … He was able to convince them that he was not at that point a danger to himself or anyone else.”

Looking back, “we certainly, you know, wish that we could turn the clock back and maybe change some things,” Brown said in a separate interview on CBS’s Face the Nation.

But at the time, there were no grounds for placing Rodger on an involuntary hold, an order which allows authorities to commit individuals to a mental health facility for further observation, Brown said.

Rodger stabbed to death three men in his apartment, before going on a shooting spree nearby and killing two young women and another young man. Another 13 people were wounded in the attack, two of whom remain in “serious condition,” Brown told CBS.

Questions about how Rodger was free to carry out his bloody assault have swirled after it emerged he left several manifestos in print and videos posted online explaining his motives, some of which were posted weeks before Friday’s rampage.

Rodger, who had been diagnosed with Asperger syndrome, wrote about his meeting with police in a 140-page manifesto-autobiography titled My Twisted World.

He said the police asked him if he had suicidal thoughts and he “tactfully told them it was all a misunderstanding, and they finally left”.

Rodger, son of Hollywood director Peter Rodger, wrote that he feared the police would discover the cache of weapons and bullets hidden in his room and arrest him.

“If they had demanded to search my room … that would have ended everything,” he wrote.

“When they left, the biggest wave of relief swept over me. It was so scary.”

In a nearly seven-minute long YouTube rant titled Elliot Rodger’s Retribution, the shooter, sitting in a car, complains about women who rejected him, and vowed to “punish you all for it”.

“I’m 22 years old and I’m still a virgin. I’ve never even kissed a girl,” he says.

“I don’t know why you girls aren’t attracted to me,” he asks, “but I will punish you all for it”.

Police recovered three nine-millimetre semi-automatic handguns from the BMW – all legally purchased and registered – and Rodger had dozens of unused rounds of ammunition.