Why? Since you & Turnbull have been discussing how it WAS done in the true-life Mafia world.

The thing about The Godfather is that besides being about a Crime Family...it is about a Family. Father, sons, daughters, husbands, wives, even Godsons. Without that, it would've simply been another mob story (not that there's anything wrong with that...).

And that's why it HAD to be Michael doing the shooting.

That's also why, when making the movie, FFC wisely kept the primary focus on the Corleones themselves and steered clear of the background stories of other characters...however interesting they may have been in the original novel.

Apple