well he's not totally bonkers then.
He's not bonkers at all. That's what makes it so chillingly terrifying.
He's spent the best part of ten years planning this, cynically considering all possible outcomes and obstacles underways. Several traits usually connected to psychopathy are displayed: delusions of self grandeur, pompous and grand visions and plans, paranoia (although not so much on a personal level, but more in a "the muslims are out to destroy my culture and the government deserves to die for abling them"! kind of way), extreme ego centrism, megalomania, total lack of ability to connect with other people on an emotional level, lack of empathy.
The last two might go some way to explain how he managed to end up capable of doing (and indeed doing) such atrocities. He's made himself unavailable for other persons, other thoughts, never exposing himself to alternative ideas, never having his increasingly twisted world view and ideas challenged.
All his actions has been deliberate and considerate, leading up to this expressed goal. The thinking behind is obviously perverted and insane, but the guy himself? He knew exactly what he did. All the way. One cold, cold fish.
That's really what gives me the shivers.