What's likely about the Rocco theory? Where's the evidence, or even the inference that he was involved?

I don't think it's important to know WHO the assasins were. I think we're told they were just hired guns. And it's fairly obvious (at least to me) that it was Roth who ordered it. (Fredo: "I didn't know it was going to be a hit", plus his involvement with Roth & Ola: "You guys got me in enough trouble already").

But the question remains: Who killed the assasins?
If it was Rocco, there would have had to of been witnesses-there were guards and such running around all over the compund after the shooting.

Michael says to Tom something like "Unless I'm mistaken, they're dead already, killed by someone inside the family" Who does he have in mind?

Also, I re-posted this to see what some of the newer members thought about this question. It hasn't been raised in a while and I figured that most newbies don't go reading topics from 2-3 months ago.