In the novel, at least, Michael includes Carlo among the suspects. So maybe Vito figured Tessio and Clemenza would stay loyal to him, so that Carlo would the one again.
I'm willing to bet that Michael
hoped that Carlo was the traitor. Puzo goes into Michael's thinking as well earlier in the book when it's time to decide whether Clemenza or Paulie set-up the Don. We know that Michael hoped it wasn't Clemenza because, well, it was Uncle Pete. Heck, it's not out of the realm of possibility that Clemenza or Tessio was Michael's Godfather? Clemenza is Santino's Godfather though, and being unfamiliar with Italian culture, is it common for someone to act as Godfather to more than 1 child from a particular family?
