The right quote for this question.
Scarfather, although there haven't been any posts on this subject recently, the issue of who killed the Tahoe assassins is probably the longest-running mystery on this board. Though some have posted interesting theories, I don't believe anyone has ever said that they're certain.
Some people a long time ago theorized that Rocco had some role in the shooting, and went on the "suicide mission" to whack Roth to "repent." I think someone may actually have found an earlier script treatment (there are many) that supported the idea that Rocco had some role in the shooting. My view is the same as others' here: If Michael had an inkling that Rocco was involved, he'd have been dead then, or soon thereafter. I also believe that Rocco took the kill-Roth mission as a desperation move to restore his standing in the family after Neri's relentless climb to push him and Tom aside.