Check out the video at post 1427 above. It looks like the shooter could be a home-schooled Christian.
From my perspective, this appears to be an "inside job." This isn't the actions of an indiscrimate hater. He chose the YWAM facility and then chose New Life church. They are connected (at least tangentially). If he wanted to kill Christians in general, there would seem to be other ways to accomplish that. I will bet that he's received some imaginary or real insult from YWAM and/or staffers from the church and acted on it.