My guess is that it was an investigation by police to determine whether these people had the means / desire to carry out their threats.
You know how after any kind of terrorist attack we get news stories about the terrorists making threats on Facebook or Twitter, or that they'd previously had people call the police to report them, but authorities did nothing? Then we get a wave of people demanding to know why action wasn't taken sooner to prevent the tragedy?
What happened in Germany is exactly the response that people want as an effective measure to combat potential acts of terrorism.
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Didn't realize that people making threats against others was a "different view" that deserves respect.
Is it not the job of the police to keep the peace and to protect citizens?