Well I might be wrong, but so far his reference to Elliot Rodger would seem to be the best indication of why he did this.
Men going on a murderous rampage because women won't have sex with them? That is at the core of misogyny, Alan. And male entitlement and rage.
(edit)
And caution noted. As I said, I might be wrong. But it is out there, and it has been reported on, so these are fair questions.
And even if that wasn't the specific motive, who does shit like this? Angry guys who feel it is okay to take their frustration out on other people, that's who. And there are a lot of voices shouting from the sidelines driving that entitlement.
Thx Smith. As noted above, FB has now verified the post.
It seems to me that the misogyny inherent in this mindset should qualify as a "political belief or ideology" necessary to make out terrorism. But I doubt the Crown will go there.