Originally posted by Turnbull:
Some people believe that Michael asked Carlo to confess because he wasn't certain, at the very end, that Carlo really ratted out Sonny, until he heard it from Carlo's lips. I don't believe that, but if so, Michael may have bought the ticket in the off-chance that Carlo was innocent. 
As I recall, the book says Michael had some doubts, which is why he wanted to be 100% sure and hear it from Carlo's dumb lips.
I think the ticket was just to get Carlo to relax and confess after being told that his punishment was simply exile in Nevada.
