I don't think its so likely that the culprit will be a dead guy, why? same reason i stated before, because that's a terrible finale for the suspense. Tommy's allready dead, no one will care if we find out he's the mole. I'll eat my hat if the mole turns out to be one of the dead, or a random member of the tower.

Another reason tommy couldnt have done it is, that seems like a really petty reason for tommy go to the mallers. Tommy was just a really nice kid, he was an innocent victim of the war, his death weighs down on Michael, he's that constant reminder that war has serious consequences, and making tommy out to be the bad guy would ruin that.