My question: where did this guy acquire the skills to carry out such a coordinated and sophisticated attack on his own?
Hate to be a broken record, but any possible question you'd have about the guy is answered in his Manifesto; I realize 1,500 pages are hard to go through (and the US media is ignoring it in favor of his almost content-free Facebook and Twitter pages.)
The answer: He's a smart guy who planned this for years, did a lot of research, and practiced a lot.