I don't think our killer is an Islamic terrorist. I think he's someone, probably a white male, who blames the world for his own problems and is lashing out. He's deeply psychotic, lives alone, and is immensely enjoying the new sense of power that he has.
For once, he's important, and he's getting off on it. The choice of victims is not important. Today's victim was a black man. Tomorrow's may be a little girl, not because he's looking for a girl, but because he's waiting for the precise moment to shoot, and the target is whoever comes into his sights at the time.
I think the speculation that he waited for a white van to be passing by at the time is almost certainly true. He IS smarter than most cops.
The only thing I don't understand is why he's foolish enough to leave handwritten notes for the police. His arrogance is going to get him caught, fortunately.