What he's NOT saying here is important. He didn't rule out criminal prosecution, he just ruled out Durham from doing it. The door is still wide open here to say that it was based on the information he had today.
Personally I think it's a pump fake designed to make conservatives angry so they will flood the airwaves and social media with outrage, while at the same time making Obama team (and liberals in general) comfortable when they most definitely should not be.