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Law enforcement officers who visited Elliot Rodger three weeks before he went on a deadly rampage in a California college town knew he had posted disturbing videos but didn't check them out because he seemed OK when they visited him at his apartment.

And even if they had watched them, experts say it's unlikely they would've been able to do anything.

"There are a lot of videos that might seem disturbing or offensive, depending on who views them," says Tom Mahoney, who co-chairs the Justice Studies department at Santa Barbara City College.

Only in hindsight is it clear that Rodger, 22, was an extremely dangerous young man who would go on to kill six students and himself, and injure 13 more last Friday night.

Rodger posted at least 22 videos on YouTube, including his final "retribution" video the night of the attack. YouTube took down that video — which detailed Rodger's plans and reasons for the killings — the next day, citing a terms-of-service violation.

Of the 21 videos still on the site, none are overtly suicidal or violent. Many feature Rodger driving in silence with 80s pop music — Whitney Houston, Steve Perry, George Michael and others — playing in the background, while in others he talked straight into the camera about his loneliness and despair.

It's unclear if there were any additional videos that were taken down by Rodger or YouTube.

Family spokesman Simon Astaire has said Rodger's mother became alarmed in late April after viewing bizarre YouTube videos posted by her son. She notified his therapist, who called health officials who in turn notified the Santa Barbara County Sheriff's Department. Family attorney Alan Shifman has described the videos as "regarding suicide and the killing of people." He did not respond to a query seeking clarification Friday.

The sheriff's office said Rodger uploaded his final video detailing his "Day of Retribution" at 9:17 p.m. on the day of the shootings, May 23. One minute later, he emailed a lengthy written manifesto to his mother, father and therapist that also detailed his plans and contempt for everyone he felt were responsible for his sexual frustrations and overall miserable existence.

The first gunshots were reported at 9:27 p.m. The rampage was over and Rodger dead just eight minutes later.

It was another half hour before the therapist saw the emailed manifesto and 11 more minutes until the sheriff's office was contacted at 10:11 p.m. Authorities contacted Rodger's mother and learned about the manifesto and the "Retribution" video.

Like many other states, California allows authorities to hold people in a mental hospital for up to 72 hours for observation to prevent them from hurting themselves or others.

Mahoney said these detentions are based on an individual's observed behavior, not just on a person's expressions that they intend to hurt someone.

Also, said Mahoney, the officers did not have the right to search his apartment without a search warrant or his permission, which he was unlikely to give because the guns he used in the killings were stashed inside.

"They were faced with a compliant, soft-spoken individual who did not exhibit any violent behavior or express to them any immediate threat of violence or self-harm," said Mahoney. "I'm sure these officers are second-guessing themselves. I know that I would, given the same circumstances. But police officers must respect the Constitutional rights and freedoms of all persons they come in contact with, and act within the confines of the law. Most of the time, things work out fine. Sometimes, unfortunately, they do not."

Attorney Robert Sanger, who has been practicing law in Santa Barbara for 40 years, said welfare checks are routine, and officers are often told what triggered the request.

"Certainly police officers have the ability to get on the Internet and check YouTube, but whether or not they would think it is appropriate in a particular case would depend on what information they were given about the video," he said.

Rodger took down many of his videos after his visit with authorities. While it's unclear exactly which videos he uploaded again or whether others were not reintroduced, Rodger describes being depressed and lonely without making threats or suicide mentions.

Rodger said he took down one video titled "Why do girls hate me so much" because it gained too much negative attention. In it, he laments his "loneliness and misery" and says he doesn't understand why girls are repulsed by him. "This world is so beautiful but it's so sad and depressing when I have to experience it all alone and I have to watch other guys able to walk around and enjoy their lives with beautiful girlfriends at their side," he said. Rodger tweeted a link to a video with the same title on April 20.

Rodger's parents issued a statement Thursday through family friend Astaire, saying they were "crying out in pain" for the victims and their families.

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Oskar Garcia in Honolulu contributed to this report.