Michael didn't even twig straight away that it was Roth who tried to kill Michael in his Tahoe home, believing it was someone inside not realising an outside force [Roth] was involved
If my memory serves me right, among others -
Michael tells,
1. Tom “They [Tahoe assassins] are dead already, killed by somebody close to us – insideâ€
2. Roth “Pentangeli tried to have [Michael] killed.
3. Pentangeli “It was Roth who tried to have [Michael] killed I know it was Roth†How did Michael suddenly know it was Roth?
Michael probably knew, immediately after the bullets stopped flying in his bedroom, that Roth was behind the shooting--the setup of Pentangeli as the fall guy was way too obvious. Roth had far more to gain by whacking Michael than Pentangeli did--as Frankie himself told Michael, "I don't have your head for the big deals." What obsessed Michael after the shooting was: who was the traitor in his family who was complicit in the attack?
