None of us here, one assumes, is or is likely to become involved in either a criminal or civil case involving the parties discussed. Therefore, surely we are at liberty to express whether we feel the alleged attacker to be guilty or not of the assault.
There are two wider issues here related to incidences of rape and sexual assault which are troubling.
Stepping on from Clare in France's example that smoking pot in college or engaging in any illegal or dishonest activity in the past undermines one's credibility as a witness - there do seem to be quite a few examples where people who have less than clean backgrounds have given testimony that has helped lead to a conviction for other crimes. For example, it's not unheard of for someone initially accused of a crime to be given a lesser sentence through a "plea bargain" which involves them testifying against another person.
If in a sexual assault, the victim is regarded as a witness, why should previous examples of illegal or dishonest activity automatically negate her testimony as unreliable? Is there something specific about being a victim/witness of a sexual assault that means previous examples of illegal or dishonest behaviour carry more weight than with other crimes like burglary or murder?
The other issue that seems clear is that sexual contact, regardless of the type of contact, is always presumed to be consensual until proven otherwise. The bar of "proof" is extremely high - e.g. the position of the semen sample in this case which suggested the oral sex was non-consensual and the damage to her underclothes have to be presumed to be the result of consensual sex unless there is considerable evidence to the contrary. And, it seems rare that testimony of the witness/victim will ever be considered as reliable evidence, unless her previous character is unblemished and there is other corroboration, say from a witness.
I could imagine even if there were CCTV footage of a sexual assault, the accused could argue that it was all just part of the "rough sex" that the alleged victim "enjoyed," and the cameras didn't catch the part where she gave her consent.