Killed Michael Corleone Apollonia

Did anyone in America know about Michael's marriage to Appolonia in Sicily?

This was never revealed in the film. In the book, Michael Corleone's mother tells Kay to forget him, meaning that Corleone was already married and would never return to the United States. The family in the novel The Godfather is aware of Michael's actions in Sicily.

Since the film takes out Michael Corleone's revenge on the man who planted the bomb in the car that killed Apollonia, it is clear that her death closes that thread of history.

System failed

There's a deleted scene from the first movie where Michael is seen recovering from his wounds after the explosion. He orders a hit against Appolonia's killer. So his family in America would probably have heard of it.

Mistah mix

The only problem with that is that he had no idea where the man was. In the novel, the man moved to the United States and works in a pizzeria in the Buffalo, NY area. One of the Corleone button men (assassins) enters the parlor, identifies the man by a tattoo he is known to have, and then shoots and kills him.

Sayan

@ SystemDown Mistah Mix: IMO, both of your comments are appropriate answers.

theRiley

I'm pretty sure I killed the bomb planter at some point, possibly on 'Reckoning Day'.