I understand. For me, accident is easier to understand. I can actually see something like that really happening. And then the actions made afterwares (overkill, staging of body and scene) were done out of desperation.
It also would account for their actions over the years (strongly insistening on their innocence).
It would also account for why none 3 ever talked about each other (Rudy cannot talk because he did the overkill b/c Amanda and RS couldn't bring themselves to do it, and Amanda and RS can't talk b/c they did all of the cover-up and staging, tampering with evidence, and the accidental wound, plus the whole prank idea which led to it all).
It explains everything for me.