Since we're citing the novel (often but not always a good bet for helping to resolve ambiguity), consider the following passage when Vito and Michael are conferring after telling Tess and Clem to sit tight (the equivalent of the fishtank scene):

Vito: "I'm surprised, though, that Barzini still made a last try at you. Maybe it was arranged before the peace talk and he couldn't stop it. Are you sure they were not after Don Tommasino?"

Michael said, "That's the way it was supposed to look. And it would have been perfect, even you would never have suspected. Except that I came out alive. I saw Fabrizzio going through the gate, running away."