hmm as much as i would like to agree, I think rollos did it 100%. When Shirley and Him was in the room talking, after she said, "I want to protect Lulu, and Join you." His expression changed, thus after that, that expression looked like he was saying. "No, That is My Job, you are trying to take my place?" ( almost confused ) then after that, Shirley added the icing to the cake by saying, " I want to bring back his happiness...and his little sister Nunnas too." Ok, From previous episodes, we know that Rollo can be a bit...physco; at that moment, something from his mind turned off or on, and on impulse, and rage, knowing that Lulu is HIS brother and no one elses. This self absorbed, feeling, this overwhelming emotion over-took Rollo. Almost as if he would say, "Who the Hell is Nunnally? I AM Lulus ONLY BROTHER. he is mine and no one else's." blah blah blah (lol) But yea, that preety much did it in for him.

Which would symbolize the mask falling and his true identity being revealed(?) Notice the change in his eyes,(he is pissed) and the mask fell, thus him killing Shirley. By taking her gun, shooting her, and putting it right back in her hand. Notice when she was talking to Rollo she let go of the trigger as well. Dont think its really anything more, but if it was well that would be a complete shock.