With all due respect, the ad-lib theory is easily the most implausible conjecture I've encountered on these boards. As one poster put it, a director simply will not let a fresh actor just start making up lines of that kind, i.e. lines which bear so directly on the logic of the plot (as distinguished from lines of little or no consequence to the plot). And if he does let it happen, it will be because he thinks it over and approves of it.

I also do not see why it is a flaw in the plot to have Roth engineer the Pentangeli hit in the manner described in my previous post. Turnbull argues that it is implausible because Roth was already arranging to have Michael assassinated in Cuba. But Roth already failed at killing Michael once, so common prudence would tell him that his next attempt could also go awry, no matter how airtight his planning. In other words, if by some mishap Michael eludes Roth's next attempt, he'll get nailed by the US Senate. It's insurance.