One of the things that we tend to forget about movies is production values, limits, and costs. Rocco became at some point in the movie a prominent and recognizable character who was meant to be so recognized by viewers as such. In that capacity he was sent to murder Roth.
You hit the nail on the head. But this ofcourse then also applies to all the other conspiracy theories on this board...
"It was between the brothers Kay -- I had nothing to do with it."
