I agree that's it's all conjecture,but given what we know about Mike,I have to believe that he already knew it was Carlo who set up Sonny. I liked the way he let Carlo believe that all he wanted was for Carlo to tell him if it was was Tatt or Barz. Of course, the answer wouldn't matter since they were both dead by then. The supposed purpose was to get a witnessed confession. (I've always had an issue with mike's "need" to get Carlo to admit what he had done. IMHO,Carlo was a dead man no matter what he said).

Carlo was really naive thinking that his only punishment was being "out of the Family business".