Megolomania - at some point I would expect him to either try to communicate with the public or press
In light of the tarot card, I guess I hit this one on the head.
As far as the tarot card, I suspect the police leaked this, meaning they have no good leads whatsoever. It's a subtle plea to the public, without coming out and saying they are stumped.
If this is the case, I bet the message was either different, or more, than what was released. Possibly more like "I am the Devil." Or something much more rational than "I am God." If the shooter believes he is being misrepresented, either by being made to look like a "nut" or by confusing his allegiences, it may prompt him to step up communication. He may make the next one to the media in an effort to get his "story" out. That can be helpful in catching him, or at least getting a better profile. Remember the Unabomber.