Let's change this scenario just a teensie weensie bit.

Let's say a cop (undercover or otherwise) was found selling some drugs and/or engaging in other FELONY level actions. A group of citizens decided they were going to place him under citizen's arrest. One of them happens to have a taser that they fire at him and it fails to serve it's purpose. The cop then reaches for his waistband and 9 shots are fired at him, one hitting a bystander, killing them.

Who would you then say was guilty of the bystander's death?

If you say the guy who fired the gun, you're absolutely correct.

If you try to argue about authority or this or that defense, you are wrong. In ALL, read that again, in ALL cases of use of Force, EVERY SINGLE LAW ENFORCEMENT BODY is REQUIRED by policy to do whatever limits the risk of potential by standard harm. This means letting the guy get away, if the cost of shooting him will result in a bystander possibly being hurt. Yes. It IS better to let the criminal go than to have an innocent person gunned down by a trigger happy cop.

When I was a correctional officer and we had to escort an inmate to the hospital for treatments, we carried side arms. Yet, we basically had an understanding that if you were to ever use that sidearm, even to prevent that inmate from escaping, inside the hospital, you might as well turn around and place your hands behind your back then and there.

Why? Because of the risk of hitting bystanders. You would NEVER be justified in discharging your weapon in such a scenario.