A lawyer of film director Peter Rodger says the family called police several weeks ago after being alarmed by YouTube videos posted by his son "regarding suicide and the killing of people".
The attorney said police had conducted an investigation and interviewed the man. Police said the man appeared to have trouble making friends but did not find a history of guns.
Police have not formally named the suspect, who died following the attack.
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Police chiefs said the suspect detonated a device as he was being pursued by police.