What strikes me most about this is how rational and non-random the targets were, if you start from Brevik's twisted premises. Kill as many of the enemy as possible when they're still young.
That they were children didn't give him pause; it seems to have been the entire point.
I've been worried about xenophobic extremism turning into violence for a while, but I thought it would be something crude and obvious, like the Malmo shooter (who only managed to kill one person, though he wounded many). I thought ultranationalists were all stupid. This is acute tactical intelligence, horrifically perverted.