A German police officer was fatally shot in 2010 after failing to identify himself when his manipulation on the door had alerted the known-armed subject of a planned search. The shooter was (eventually) acquitted. Though the circumstances were rather unusual, the court noted that in that specific case, the inability to ascertain the nature & extent of the threat within available time made acting this way based on his assumptions excusable.
https://www.bundesgerichtshof.de/SharedDocs/Entscheidungen/D...