I have never bought into the theory that Rocco was involved in the ht on Michael in any way. I see no evidence whatsoever of this in the film, but merely speculation on these boards.

The truth is Rocco was passed over by Neri, plain and simple, and because he was expendable to Michael, and because Rocco was eager to please Michael he volunteered to kill Roth.

If anyone killed them it had to be Fredo who was in on it as I have posted elsewhere. Remember that Deanna was shrieking that something happened right utside "her" window.