If I am not mistaken, there has been some discussion in the past as to whether or not it's even Rocco who makes the comment, since it is made off-screen.
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Originally posted by Caesar's Dealer:
Yes, he was trying to put suspicion on Pentangeli.
It wasn't Rocco (or whoever made the comment) who was trying to shift the suspicion to Pentangelli, it was MP and FFC.

"Difficult....not impossible"