To Apple's point: The novel flat-out says that, after finding out about Sonny's murder, Tom "knew now that he was no wartime consigliere...old Genco would have smelled a rat." True, he couldn't have stopped Sonny on the causeway and did dispatch men to follow him. But Tom, a lawyer and not a Sicilian, saw things too rationally. Seemingly it didn't occur to him that Carlo would burn for revenge after Sonny publicly humiliated and beat him. Rationally, Carlo should have recognized that he'd never get away with it. But rationality had nothing to do with it. As Vito said (in the novel): "Vengeance is a dish that's best eaten cold."