The LA Times spoke to a family friend who said Chin Rodger's therapist told her to check her email just after 9 p.m, "Have you gotten Elliots email? I think you should see it." After seeing the email, Rodger then "immediately checked Elliots YouTube channel, where he had posted bizarre videos about how alienated he felt, particularly from women" (transcript of the "Retribution" video) and called her ex-husband to alert him. The friend, Simon Astaire, told the Times that both Chin Rodger and Peter Rodger rushed to Isla Vista, with Chin Rodger "call[ing] either 911 or the sheriff directly,
and arranged to meet with authorities when they arrived."
http://laist.com/2014/05/26/alarming_email_prompted_elliot_rodg.php