Just like who opened the drapes and who killed the would-be assasins...it's one of those holes, those never-to-be-answered questions that personally I hadn't really thought about and that FFC/Puzo assumed would never be asked 30 years later.
Which I think is a more crass way of agreeing with Turnbull's theory # 2.
And now Turnbull...you can present your 'longer' theory.
Apple