Elliot Rodger
The Isla Vista guy who wrote his "unreliable narrator" personal account of why he was so mad at the world
Can't help thinking of this film in retrospect - both situations where the parents (only the mom in this film) were aware there was a problem but either didn't try hard enough to address it, or perhaps tried as hard as they were able - and just weren't able to address the kid's actual issues.
Maybe they weren't even addressable - Rodger's screed shows what a warped, narcissistic view of the world he clung to, maybe he could never have been disabused of it.