Yeah, there was a news article in the last couple of weeks about that very thing. Apparently the Baltimore PD have been marking rape reports as unsubstantiated because, at least in one case, the woman didn't fight back under verbal threat. There is something funky with the law either in MD or in Baltimore (don't remember which) that requires the rapist to actually do violence (apparently the unwanted penis isn't enough) for the rape to be counted as a certain type of sexual assault. So all the would be rapist has to say "if you fight back, I'll kill you", the victim believes the rapist and doesn't fight back, and bingo-bango under the law, the rape is unsubstantiated.

In at least one case, a serial rapist rapist walked free because he had no prior history of sexual crimes. Because prior reports were unsubstantiated since the prior victims didn't fight back.

Tried to find this article without joy. One of the bajillion I come across via RSS.