“When people dress up as Adolf Hitler, an investigation is always necessary,” a spokesman for Saxony police told news agency DPA on Monday.
The fake Führer appeared at a classic motorcycle gathering in Augustusburg, near Chemnitz, and was seen in videos of the event posted online.
He sported a toothbrush moustache and was seated in the sidecar of a bike driven by a man dressed as a 1940s-era soldier, complete with World War II-style helmet.
People are heard laughing as the pair pass by and a policeman guarding the event pulls out his phone with a smile to take photos.
The officer could now face consequences for his failure to step in.
“We would have expected our colleague to put a stop to all this without the least hesitation,” the Saxony police spokesman said.
The officer seen laughing at the impersonator was summoned for a meeting with his superiors and has “acknowledged his misconduct”, a spokesman for the local Chemnitz police told AFP on Tuesday.
Saxony premier Michael Kretschmer also condemned the Hitler pantomime.
“Dressing up as a mass murderer is more than just bad taste,” he tweeted. “This kind of behaviour is unacceptable and shouldn't be repeated.”
Bikertreffen auf #Augustusburg: Auftritt als Massenmörder ist mehr als geschmacklos. Bin mir mit Bürgermeister Neubauer einig. Wir wünschen uns 2021 das 50. Treffen. Zuvor muss klar sein: So ein Verhalten ist nicht akzeptabel & wird sich nicht wiederholen. https://t.co/QArT3DTbI6
— Michael Kretschmer (@MPKretschmer) January 13, 2020
Around 1,800 motorcyclists and 7,500 visitors took part in the weekend classic bike festival in Saxony, a region in former communist East Germany that has made headlines for far-right and neo-Nazi activities in recent years.