It could be the false accuser told SANE/LE she had sex with her boyfriend in the day/s before the party, and a DNA sample was taken from him to distinguish his "consensual" contribution from their "forcible" contributions. He may not have a record, but given her known paramours he probably does.
That's true; the Durham cops have got to be feeling embarrassed over this prosecution because it makes them look bad since most people don't know that the DA has been using his own investigators and pressing ahead despite the evidence.