I've never cared personally for the Riley as the rat theory, but here is something I just thought of. If she is the rat, perhaps her and Scratch have some kind of romantic history together?

Also, can anyone recall if Pippen has ever seen Riley before? Pippen clearly recognized his shooter, if he has had a pleasant encounter with Riley before I think that dumps the Riley as the shooter theory into the waste bin.

Also, I just want to toss something out there to the community. If the shooter is loyal to the tower why would they have shot the radio as well?