Old_Geezer - //It doesn't explain how he knew there was no threat, that the gun wasn't loaded, and it was a "suicide by cop" situation. //
I don't think that is what the officer was saying. Obviously he had no idea of knowing if the gun was loaded or not, but his approach was based on the knowledge that he may be facing a loaded gun, but he made a judgement about his ability to defuse the situation.
Sadly, he had no way of knowing if his approach would have been successful or not.
// I suspect an internal discipline option would have been better than firing the guy. Seems to me that it turned out he was right, although lucky to be so. //
As I said in my original post, I don't think that the fact that the gun was not loaded is an issue - the officer behaved without that knowledge, and made a judgement based on the situation he faced, and that should be accepted.