Surely if this is what DM or MS is going to postulate, one of them will have to take the stand to explain such a position, IMO.
If the Crown present the totality of the evidence without placing either DM or MS as the shooter specifically, but instead rely on the relationship of all of the circumstantial evidence, I would think the Crown will have successfully made their case beyond all reasonable doubt and then one or the other - or both - of the accused would have to say something to challenge the Crown's case or just take their chances and accept that they will likely both be held responsible and therefore convicted of the crime, IMO.
If either defense for MS or DM rests without saying something to counter the Crown's case, I think both are doomed, IMO. They will be foolish to think the jury would come to the conclusion that neither of them killed TB, IMO, once all the evidence is presented. I keep thinking big picture, and I hope the jury is too.
All MOO.