Originally Posted by Pax
The problem starts further back than that, with a lackadaisical approach to the Four Rules. Once you start saying things like, "In the real world you won't always have time to identify your target..." -- you're headed for a mess like this. Low expectations about safety tend to lead to poor safety performances.
We shouldn't forget that Cooper's Four Rules were originated for an active combat environment. Of course they are of great benefit all the time. That doesn't change the fact of why they were originated. The incident described in the OP, was exactly the kind of thing Cooper was trying to help prevent.
RULE I: ALL GUNS ARE ALWAYS LOADED
RULE II: NEVER LET THE MUZZLE COVER ANYTHING YOU ARE NOT WILLING TO DESTROY
RULE III: KEEP YOUR FINGER OFF THE TRIGGER UNTIL YOUR SIGHTS ARE ON THE TARGET
RULE IV: BE SURE OF YOUR TARGET
If you can't positively identify your target, you're not supposed to fire. Period. Shadowy figures, glimpses, noises, etc aren't known targets and should not be fired upon.