I always felt it was a spur of the moment thing. Tony wasn't sure, but then Ralphie grew tired of the inquiries and started taunting him. Next thing you knew they were fighting and that was it. But this murder bothered me more than any of the other killings in that show. Not because of the brutality or anything like that, but because of losing this character. Ralph Cifaretto was to me, the most interesting guy on that show.