When Michael tells Carlo he will be his right hand man after their move to Nevada, Carlo before he leaves, thanks Vito and Vito responds with an affectionate “I’m happy for you, Carlo”

Had Michael and Vito already worked out Carlo’s role in Sonny’s death? More so, did Vito know before Michael or because of his continued case of slipping, had it not dawned on him yet?

The hero and the coward both feel the same thing, but the hero uses his fear, projects it onto his opponent, while the coward runs. It's the same thing, fear, but it's what you do with it that matters. Cus D'Amato