Context: Attacks on Refugees
In the first three quarters of 2015, there have been 505 attacks on places where refugees live.
Until the 7th of December 2015, that number grew to 817.
These numbers do include things like Volksverhetzungen or smaller property damages, but officially, 130 are classified as violent, among them 68 arson attacks. This official count is somewhat disputed, the Zeit for example classifies 222 of the attacks as violent. 104 people have been injured in these attacks, but luckily there have not been any deaths yet (that I know of).
Here, you can find a list of attacks.
For context, it should also be noted that there was a wave of attacks on refugees in the 90's, which resulted in a number of deaths and which is still remembered by many.
The current - and former - attacks on refugee centres are important for context, as it may change how police handle information, as there is a real danger that certain parts of the press will exaggerate the amount of crimes committed by refugees, which could result in even more attacks. It also makes it important for the police to handle information accurately, which may delay the issuing of press releases.
Context: Police and Media
The police in Germany does not have to volunteer information; they have the right to keep information private, or only disclose it in response to direct questions.
If the police have a valid reason, they also have a right to withhold information, even in response to direct questions.
For example, the police may withhold information if it helps them to combat terrorism, or if releasing information may interfere with catching criminals (see for example Polizei und Presse: Rechtsprobleme der polizeilichen Öffentlichkeitsarbeit), or the different laws of the states (Landespressegesetz).
Answer
There have been a number of accusations that the police is not volunteering information, but I am not aware of any accusations that the police is not giving information when it is requested.
Basically, the scandal is not that the police are not issuing press releases for every crime - because they just don't do that, because there is no public interest, and it would be way too many - and the scandal is also not that the police withheld information when directly asked, but the issue is that police may have been instructed not to issue press releases for crimes in connection with refugees in general, or that they have been instructed to check if it is actually necessary to issue press releases for these cases.
- Hessen (Frankfurt, the case you mentioned): The minister of the interior denied the accusations (source). You can find the original tabloid article here, but it should be noted that Bild is not known for always being the most accurate newspaper. Still, even Bild says: "Jedoch: Ohnehin wird nicht jede Straftat in Deutschland automatisch veröffentlicht", which basically means that a press release is not made for every crime anyways.
- Thüringen: A newspaper cites from an email from the director of the police: "[Bei] Einsätzen in den Unterkünften, die keine Außenwirkung erzielen [sollen] keine Pressemeldung gefertigt [werden, nur ] bei eventuellen Anfragen [von den Medien soll Auskunft gegeben werden]". This basically means that police should not volunteer information, except if the event had visibility or if the media asks about it themselves (which is more or less how most cases are actually handled anyways, so if such an instruction existed, it basically says to handle crimes of refugees like crimes of anyone else). (source) (source). These accusations have been denied by the minister president. (source)
- Schleswig-Holstein: A newspaper accused the police of not issuing press releases when crimes happen in connection with refugees. The police denied these accusations, and said that the seriousness of the offense and the current state of information are deciding factors for when press releases are issued. (source) The newspaper also alleged, that they were told not to report an exact list of crimes committed by refugees, as it might cause violence against refugees.
