The only mystery is: Why didn't Vito know earlier that "it was Barzini all along"? As he told Tom, "Tattaglia is a pimp...alone he could never have outfought Santino." Tattaglia had always been a pimp--didn't Vito know that before the meeting? And, shouldn't Vito have known that Barzini was the number-two Don, and that he'd have the most to gain from the drugs deal, and from eliminating Vito?
Because the Don, rest in peace, was slippin.
