The Rosato brothers attempt to kill Frankie Pentangeli telling him just before they garot him, "Michael Corleone says hello" to make him think that it was on Michael's order (when in fact it was Hyman Roths). For what reason are they lying to him? This lie only serves a purpose because he's left alive and ends up testifying to the senate commmission because he thinks Michael has betrayed him. But that's all accidental. Its pretty obvious that they are KILLING him when the cop walks in by chance and the whole thing goes to hell. Then what was the purpose of lying to him at the begining?