We don't do ethical questions here, that's what Philosophy SE is for (it might even be a FAQ). Legally, the later bombing is irrelevant. If Jones beats Smith, and given the law that A cannot beat B, Jones is guilty of assaulting Smith, even if a preponderance of evidence indicates that something else might have happened "if not for". Jones would not be allowed to argue that he is innocent because "if not for my assault, Smith would have died", at least in any existing jurisdiction that I have heard of. Theoretically, the legislature / parliament / king could declare as a matter of law "It shall be a positive defense that result X would have happened if action Y had not taken place", but that has yet to happen. That would seriously undermine mens rea as a crucial element of criminal law.

We don't do ethical questions here, that's what Philosophy SE is for (it might even be a FAQ). We can deal with the legal implications.