elliot rodger, the killer in santa barbara. i wonder, have people read this manifesto? how many people have read the manifesto? you go and read it and several places in there, i'm just going to read you one, he explicitly talks about why he picked a particular place to go and attack. and so here he says, another option, deltopia, a day in which many young people pour in from all over the state to have a playa break party on dell street. i figured that was a perfect day attack isla vista but after watching youtube videos of deltopia parties, i saw there were too many cops walking around. i felt it was impossible to kill enough of my enemies before by thosepatched damnable cops. he's essentially saying -- and if you read this, the guy wants attention, he feels he's not given the proper attention, he wants to give as many people as possible but worries that with multiple police officers there he'll be stopped because they have guns and they'll be able to stop him. the monkton, new brunswick killer in canada. this is from his facebook page. i don't know if anybody has looke

. >> reporter: peter rodger's son, elliot, was only 22 when he died, taking six other lives with him.lled manifesto he left behind provided a rare glimpse into a mind broken by mental illness. >> i don't know why you girls aren't attracted to me. but i will punish you all for it. >> reporter: what's the most shocking revelation to you? >> that he could hide. that he could hide these feelings from everybody. i can't wrap my head around it. >> it's extremely difficult to predict future violence. people have spent their careers looking at ways to predict violent behavior. and we're terrible at it. really the only prediction of future violence is past violent behavior. again, in this case there was apparently no evidence of that. >> reporter: but inside that shy, quiet young man was hidden rage. elliot's journal documented a master plan of revenge, once writing, "if i can't have it, i will destroy it." andrew solomon has studied the patterns between mass murderers at columbine and newtown. >> in neither instance was the mass killing something that happened on the spur of the moment. it wa