Old arguments don’t go away merely because they are unfashionable. I could argue either way on capital punishment and the prospect of executing innocent people weighs very heavily indeed with me, but I find this argument difficult to answer too:-
A enters a corner shop, pulls out a gun and shoots shopkeeper B. A then runs off, but the whole thing was recorded on CCTV. A is caught, tried, found guilty and sentenced to life imprisonment.
C enters a corner shop, pulls out a gun on shopkeeper D and shouts "you're a dead man". He acts as if about to fire on D, but D grabs hold of C and in the ensuing struggle C is shot dead. The whole thing was recorded on CCTV. Later in court, D is judged to have shot C in self-defence.
One person dies in each scenario, but in the first scenario it was an innocent victim B and in the second it was assailant C. In other words, the wrong person died in the first scenario and the right person died in the second.
Why shouldn’t the law assume that in similar circumstances, B might have killed A in self defence? Why doesn’t the law rectify the situation whereby B’s right to self-defence was unavailable, overpowered by the assailant or otherwise not exercised? In other words why not execute assailant A as retrospective self-defence on B’s behalf?