Here's what's up. If this turns out to be locals such as right-wing extremists, this is going to be a big backlash worldwide against the US "Americans" killing their own. This is going to be a huge PR disaster. So Bush is minimizing the damage as much as possible by keeping the idea out there that it could really be locals after all.
That's a clever thought, though it sounds a little too Clintonian for Bush. I hope you're wrong about it being domestic.