IMO this thread needs to be broken up into several or at least have some defined situations.
Situation 1: Aurora- Man is by himself with a CCW. He is in no danger, has no family to protect. He wants to play hero. He engages the BG and the result is he drew fire to his area which was not under fire resulting in the deaths of 1 or 2 folks. He shoots at the BG unloading his magazine and kills the BG but kills an innocent bystander (no richochette, just a miss)-I think the guy needs to be hauled off to jail becasue of his actions he was part of those people dying.
Situation 2: Aurora: You are fighting for your life, BG is laying down fire in your direction. You are honestly and rightfully in fear for your life. You shoot back, missing, killing 2 folks. You end up killing the BG. I can't speak for the law in all 50 states but I do not think this person should be at fault. He was under fire, he was being targeted by the BG. He did the only thing he could.
Situation 3: BG is holding a bank full of people hostages (or terrosists holding hostages, either way). They execute one hostage and say they will execute more. You do not know if or when a rescue plan will occur. These are pretty stupid terrorsts and did not check folks for weapons. Time is coming up for the next execution and it is not you. But you feel the need to act. You get up and lay down fire killing all the BG's and two hostages. (let us say 15 survive). I think you acted accordingly.
Situation 4: Let us use the old gentleman n the internet cafe for the second to last situation. He felt his life was in danger though some might say otherwise. He shoots at the BG's but in the process hits and kills a bystander. Toughie. I do not think their lives were in danger and statistically a robbery like that does not end up with folks getting killed unless there is resistance. But that is up to the mindset of the person there. But I would say he is not responsible.
Situation 5: Same as #4 except the old man did not feel his life was in danger and wanted to play hero. He shoots BG's and kills a bystander in the process. He is responsible. IMO