It is mostly people in Russia who are claiming that the Berlin police and prosecutors are covering up the rape of the 13-year-old girl, but it is more likely that there is not enough evidence to support the claim. Russia just doesn't have a good past of doing things for other than political purposes.
No the dismissal of the 13-year-old girls rape was not a police cover-up. Rape cases are notoriously difficult to prove even under the best of circumstances, and this case had many evidentiary hurdles. Additionally, due to the sensitive nature of rape cases, the public can not be privy to certain details that may have led to the dismissal.
There is no supporting evidence of a police cover-up involving the kidnapping or rape of a 13-year old girl from Berlin as stated earlier this week. The cell phone tracking placed her with a friend at the time of the alleged kidnapping and there was no evidence of sexual assault.
If there is not enough supporting evidence to support the crime listed at hand, it is not necessarily a cover up. There could be a multitude of reasons behind whether or not a person can be convicted of a crime and if there is not enough evidence to support going to trial, a case could be dismissed.