At that point, the Roth/Michael power struggle was in its last round, and time running out on both of them. Roth's plan was to whack Michael right after the New Year's celebration, and Michael knew it. Only hours remained for both of them: for Roth to get the $2 million, for Michael to find out who the traitor was, whack Roth, and get out of Cuba alive. Fredo delivered the money, but Michael hadn't handed it over. Why? Roth demands to know if "you're pulling out." If so, he's got to move up Michael's assassination. Michael's on the defensive: "I just wanna wait..." He knows this is a feeble response, and that his life could be on the line. So he shoots back, "Who had Frank Pentangeli killed? I know I didn't." IMO, it wasn't a real question--it was an attempt by him to put Roth on the defensive. Roth made an overpowering reply in that famous soliloquey--watch the look on Johnny Ola's face and you'll see that he thinks his boss showed up Michael for the wimp he was.

But the marvel--the genius--of that scene is that it shows us two powerful men digging in at the last minute for what they want: Michael for more time to find the traitor, Roth for his $2 million. It's also a terrific little throwback to a key scene in GF: When Roth tells Michael that Moe Green's murder "had nothing to do with business," do you believe him any more than when Michael told Sonny that his plan to whack Sollozzo and McCluskey was "business, not personal"? Crime titans that they are, Michael and Roth are still people with emotions.