As people have mentioned before, the media is absolutely horrible about objectively reporting about what happens. People have this nature to try to find justification about the unknown, the stuff that scares us, and what would drive someone to do something, and then they latch onto ridiculous concepts as what a person enjoyed, as if it's what caused the tragedy in the first place. It's somewhat dangerous to go and try to look up videos of a guy like this and try to see trends or a pattern in what led to him doing such terrible things, but the blunt answer is nobody can really know what set the person off except for that person alone. People are complicated, and I doubt anyone's going to find a satisfactory answer that would fit neatly into clear and non-muddled motives with something like this. Don't be so quick to assume you know what drove this man to kill, as whatever clues were left behind might as well be purely circumstantial. 

Just let the investigators do their job. Life rarely gives you all the answers you want, no matter how desperately we want answers and closure, and whatever comes of this likely isn't ever going to prevent a similar person from also deciding to take another person's life.