And how is it self-defense for the cops to kill the person who is NOT shooting at them? Charge them with manslaughter and let a jury decide if they were justified.
https://en.wikipedia.org/wiki/Transferred_intent
Intent follows the bullet. The intention of the shots were to disable the gunman. The self defense firing towards the gunman will apply self defense to a bystander in the line of fire.
It does not follow if you are firing wildly, which is the claim of the grand jury.