I'm going to have to agree with Jaylan. Huge entitlement and narcissism caused by real problems in his life that he spun out of control.
Reading through his manifesto
-He hated blonde guys and was jealous of good lucking muscular men
-He hated blonde women because they dated everybody but him
-He hated his black friend because he lost his virginity at a much younger age than he did
-He hated his hispanic friends because they had success with women
-He hated his fat Jewish friend who managed to get laid
-He hated his parents for getting divorced
-He hated his mother for not marrying somebody rich
-He hated his heritage because he felt it made him short
His life was filled with hate and jealousy. He could never see the good stuff he had in his life. Despite the fact that he gets free BMW from his mom, free clothing at Nordstroms which is decently expensive, expensive watches, the dude was drowning in money for only being a college student. I had a friend with two doctors as parents and he never even got as much stuff as this kid did!
And this kid isn't even ugly. Sure he is shorter than average from what he seems to be saying, but I've had uglier and shorter friends than him get relationships and get laid. Not to mention he has his parents giving him whatever he wants lol.
Here's what I think. His mother pampered him as he was growing up, giving him free stuff all the time. He thought he deserved everything to just fall into his lap. It didn't, because you actually have to work on relationships, not just stroll in and redeem your free blonde girl card. He hated half of his self. He hated the fact that he was half asian instead of full white. When you have a deep ingrained hatred of yourself, combined with hatred of your family and envy of other people's families, genes, girlfriends, then I would expect him to go crazy. I believe somewhere in his manifesto his mom or step mom made fun of him for still being a virgin. That's really ****ed up.
But this is the part that's most messed up. This kid met with police and therapists multiple times people he went on his rampage. At the end of the sessions they concluded he was OK and had no danger. I wonder what the actual threshold would be for a therapist to say this person is really ****ed up and we need to correct/help him.