From a Time magazine article written decades ago:
“A door opens and a police officer is suddenly staring at the wrong end of a gun. In a split second, his brain is hyper-focused on that gun. It is very likely that he will not recall any of the details that were irrelevant to his immediate survival: Did the shooter have a moustache? What color was the shooter’s hair? What was the shooter wearing?
The officer’s reaction is not a result of poor training. It’s his brain reacting to a life-threatening situation just the way it is supposed to — just the way the brain of a rape victim reacts to an assault. (emphasis mine) In the aftermath, the officer may be unable to recall many important details. He may be uncertain about many. He may be confused about many. He may recall some details inaccurately. Simultaneously, he will recall certain details — the things his brain focused on — with extraordinary accuracy. He may well never forget them. All of this, too, is the human brain working the way it was designed to work.”