A police officer in Göttingen is suspected of having used excessive force during a mission because of a disturbance of the peace.
A video of the incident is circulating on the net, the authenticity of which there is no doubt, as a spokeswoman told SPIEGEL.
The investigations are already underway, the officers deployed have been determined.
Criminal proceedings are pending against her for assault in office.
The Göttingen police spoke on Twitter of an "unacceptable incident".
According to the police, the officers were called into the apartment of a 19-year-old on Thursday because of a disturbance of the peace.
A video shows the teenager talking to one of the officers, after which the policeman hits him in the face with his hand.
The sequence is only 13 seconds long, but does not show any physical attacks by the 19-year-old.
On request, the spokeswoman could not say whether he had previously physically attacked the officers.
That is also the subject of the investigation.
According to "Frankfurter Rundschau", the video exists because the young man was logged into the Discord chat program at the time.
Another user recorded the conversation with the 19-year-old.
Since the 19-year-old's microphone was switched off, it is not possible to hear what he said to the officers.
According to the spokeswoman, the officers deployed are Göttingen police officers.
The video was found on social media and the first investigations were initiated "immediately".
The video was assigned a specific mission.
It is still questionable which of the officers carried out the blow.
Due to the position of the camera, neither name tags nor heads of the police can be seen in the video.
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