This situation just occurred today.
Here's a link to the news story.
At least 50 shots fired at Fashion Island. Shoppers started screaming and scrambling | police, area, island - The Orange County Register
A man apparently was firing into the air in the parking lot just outside a major mall in So CA. It appears he was deranged or trying to commit suicide by cop, but, what would you do? Let's pretend you were located at the point where the video is shot from.
The guy was apparently shooting into the air, however at the video distance you can't tell. On the surface he's obviously a clear danger to everyone around, and it only takes a split second to fire at someone as opposed to into the air.
It would be hard for anyone to convict someone for taking him out, when hundreds of people were put into danger (even in SoCal). However in this case apparently officers were rapidly on scene - what would you do if you were responding through the parking lot with a gun in your hand? Very easy to be mistaken as a second shooter. Even with a CCW (not that you could get one in SoCal) it would take some fast talking.
What do you see as your responsibility to protect others in such a situation? Here is a man who on the apparent surface is threatening hundreds of people with deadly force, an easily justifiable use of deadly force. But perhaps in reality he was mentally ill, or despondent over something and trying to get attention or to get someone to shoot him.
What if you shot him in self defense of others, and then discovered he really wasn't much of a threat, or that he was trying to achieve that outcome?