Originally Posted By: Buttmunker
But isn't it possible that the organization of the hit was done without Carlo being willingly involved?


No, it's not at all possible. As was posted earlier, Carlo openly admits that Barzini approached him to set up the hit on Sonny:

Michael: Now who approached you, Tattaglia or Barzini?

Carlo: It was Barzini.

It doesn't get any clearer than that.