Quick question on The Godfather: The Game Storyline

[mvp828]

So I finally started playing this game after getting it cheap quite a while back. I am done with all the story missions, but I some how missed the part of where Don Vito Corleone was killed (or went into hiding?)... Who, what, when, where, how, and why?

I cannot figure out for the life of me when he got killed, I remember him in one mission at the meeting where he pleads truce with the other families and then the next thingI know Sonny is ordering me around.

Thanks