I was a cop. I’m fully versed on Qualified Immunity.
It covers that if they’re doing their jobs according to the law, then they are immune from civil actions. If, during the event, they broke the law, then they can be sued and also charged with a crime.
If a law enforcement official says that he’ll only answer a question if he’s given immunity, that should be raising a tsunami of questions as to what happened.
For the reasons that you expressed. The officer believes he has acted outside of the law. Oh well. Just another day on the job. Deed done, no reversing that, and no consequences to whoever "pulled the trigger," other than (maybe) a tounge lashing. He'd do it again.
This isn’t a police world where the citizens are messing up. This is a people world where the police are messing up. The police department’s rules are meaningless. There is no immunity, ever.