I'm also wondering if Riley didn't splash herself with a little booze after the shooting to throw suspicion off herself. As much as I don't want Riley to be the traitor, the evidence does seem to be mounting:
(1) She met
Michael and
Angel in the stairway, and could have been fleeing the scene.
(2) Of all the suspects without alibis, she had the best opportunity to steal the
silenced pistol (during the Lizzie rescue mission)
(3) Unlike
Victor, who I seriously doubt is the shooter, she's been there the whole time so could have been the original rat.
Kelly is still a possibility, and my original choice for the rat. But Riley is moving up my suspect list quickly.