It doesn't but it's the only explanation that holds any water, as Fredo was the only one that had both access and motive.
But that doesn't seem to be exciting enough for some so they start up with all kinds of wild and convoluted theories.
Which is what generates excellent debate. Without those theories this part of the forum would have been mute.
No matter what you guys think, I still consider Rocco a serious candidate for being part of the conspiracy. IMO, Michael's line "all our men are business men" would not apply to Fredo, but hints to one of his caporegimes. FFC would not want the viewer to know that Fredo was in on it so early on in the film. Remember that Rocco was in charge of security of the compound, so he could go to most parts of the compound without arousing suspicion. He would have been the perfect candidate for Roth, far more important than Fredo or the Rosato brothers, as he held real sway within the organization. Rocco knew that he would always be second choice to Michael, after Neri. But even though Michael favored Neri, Rocco seemed to be in command of the muscle-end in Nevada. So with Michael out of the way, Rocco would have been his natural successor. So the fact that Rocco could potentially form a threat to Michael along with being a possible suspect was more than enough reason for Michael to dispose of him. Afterall he could simply replace him with Neri.
