Vito's death was unexpected. Surely, you don't contend that Mike was going to wait until Vito died before he murdered the Dons. Are you saying that had Vito lived to be 90 then there would not have been any massacre in '55 or '59' or '62, etc? I reiterate: one cannot plan a murder and then expect to be separated from its implementation by someone else. Law and morality do not admit to such a separation.