I open my door around three one night with my pistol behind my back.
Two of my neighbors had been fighting .
Was a officer on the other side of the door... think he was as shocked as I was. He had the wrong house, I told him where to go and he left.
NO way I'd open my door at 3am without knowing who's there. anyone that knocks on my door gets challenged by a loud "who's there" or something similar. opening your door with a weapon in hand in front of a cop is a good way to get shot. mistake or not .. that cop wants to go home and will defend himself against any perceived threats.
anyone claiming to be a cop will be verified by checking to see out a window if a patrol car is actually there before opening the door. standard tactic for thugs to claim they are say someone from PSO or ONG or whatever to get you to crack the door open.
best to challenge all knocks at your door .. home invasion thugs will typically bang on doors to find out if anyone is at home. if no one answers, your door may get kicked in .. opening up your door a crack may get the door kicked into your face. which is how a lot of home invasions gain entry.