Yes, you can't trust German police, better to trust a German affiliate of a virulently anti-PRC Chinese-language news service founded by a fringe religious organization. Next you'll be citing the Washington Moonie Times.
No, you can't trust them
either. I don't trust anything on this either way.
All media lies. That's something you just have to accept. Purposeful lies, lies of omission, white lies, it doesn't matter. You have to get several secondary sources or a few primary sources to get some idea of anything approaching the truth.
The main problem is that you can't trust any political institutions either anymore. They used to be politicised but the politicisation was opposite to the way the media was, so you could get some idea of what the definite facts of something were. Now the German media and the German police lie in the same way and you have to use crazy obscure sources to get any real sort of information about a case.
As an example, the "loony" media source says that the girl was kidnapped and gangraped. The police source says that they have no evidence she was kidnapped or raped. However, they did not state sexual activity didn't occur and they admit that she was missing for a few days. The places where these two sources overlap is where the definite truth is. The majority of the time, at least.
The primary problem is that you really can't trust anything that comes from the German police regarding this stuff anymore. Hell, I wouldn't trust the police of any European nation.
You are wasting your outrage. There are real cases to be outraged about, but this is a hoax.
Both German media and police are careful to correct and avoid the impression that they keep information back. If you read German media (which I suppose you don't), that is noticeable right now. As I said, you can find plenty of reports about sexual assaults committed by immigrants right now, even the Greens are finally officially acknowleding that. If police outright say that nothing happened, in such a sensationalized case, I'm inclined to believe them. If people here kept getting the impression they were constantly being lied to, that would be political suicide right now.
Of course if you are trusting nobody and just want to be outraged...
The primary problem is that being careful to maintain an appearance does not mean it is not going on, it just means they're better at hiding it.