ISLA VISTA, Calif. - (CNN) -

Elliot Rodger stood in the doorway, talking to sheriff's deputies who had come to check on his welfare, and worried that his plan to kill was over.

Last month, officers visited Rodger, 22, who they say killed six people and himself Friday night, at his apartment in Isla Vista, California.

"I had the striking and devastating fear that someone had somehow discovered what I was planning to do, and reported me for it," Rodger wrote toward the end of a 137-page account of his life. "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."

The manifesto, titled "My Twisted World," was obtained by CNN affiliate KEYT.

"It was apparent he was very mentally disturbed," Santa Barbara County Sheriff Bill Brown said, referring to the contents of the autobiography.

So disturbed that someone from a mental health agency, after consulting with one of Rodger's relatives, requested police check on his welfare April 30, Brown said.

Rodger's family contacted police after discovering social media posts about suicide and killing people, family spokesman and attorney Alan Shifman told reporters Saturday.

Brown said Rodger told deputies it was a misunderstanding and that he was not going to hurt anyone or himself. Rodger said he was having troubles with his social life.

"He was articulate. He was polite. He was timid," Brown told CNN on Sunday.

There was nothing in his behavior to suggest he was violent, and the deputies "determined he did not meet the criteria for an involuntary hold," Brown said.

Rodger wrote that a wave of relief came over him when the deputies left. "If they had demanded to search my room ... (t)hat would have ended everything. For a few horrible seconds, I thought it was all over."

After that, Rodger wrote, he kept one of his guns and some loaded magazines near him so if police came back to his apartment, he would try to shoot them and escape. "Thankfully, all suspicion of me was dropped after I took down the videos from Youtube, and the police never came back."

"It was all because of the videos. I must have expressed too much anger in them. I immediately took most of them off of Youtube, and planned to reupload them a few days before the Day of Retribution." Rodger uploaded a video Friday, calling it his last.

Sheriff: Plan took a year

The angst leading up to Friday's evening of horror was years in the making. The plan to kill many people apparently had come together in the past year, Brown said.

Rodger was frustrated by his short stature, his parents' divorce and his lack of success with women -- and chronicled his perceived misfortunes in his manifesto.

He picked Friday to launch a killing rampage, outlined later by police.

It started at his own home in Isla Vista, near the scenic beaches of Southern California. Rodger stabbed three men to death at his home. They are Cheng Yuan Hong, 20, and George Chen, 19, both of San Jose, and Weihan Wang, 20, of Fremont, the Santa Barbara County Sheriff's Office confirmed Sunday.

They were students at the University of California, Santa Barbara, the Sheriff's Office said. Hong and Chen were "listed on the lease for the apartment as tenants, along with Rodger," the Sheriff's Office said.

Rodger then took his handguns and went to the Alpha Phi sorority house near UC Santa Barbara campus; he hinted at the carnage he'd inflict at the sorority house in the YouTube video called "Retribution."

"On the day of retribution I'm going to enter the hottest sorority house of UCSB," he said in the video. "I'll take great pleasure in slaughtering all of you."

On Friday night, sorority members heard loud knocking on the front door for several minutes -- but nobody answered.

Minutes later, Rodger sprayed bullets at the house from across the street, Brown said.

Witness Kyle Sullivan saw three young women lying on the front lawn.