[BaDonkeyDonk]

Why haven't you called the police yet?

Rape is serious stuff. Calling the police will do a few things:
1. They'll investigate it and get both sides of the story.
2. She will be provided with rape counselling.
3. Even if he is innocent of actual rape, the fact that he attempted to have sex with a passed out girl is reprehensible and he deserved the reputation and any press coverage.

Other points:
1. Depending on the specific laws in your area, this may or may not have been actual rape (usually penetration is required). However even attempted rape is just as bad legally.
2. I'm not a lawyer, but I'm pretty sure that the concept of the victim being required to 'press charges' is long gone. Anyone can report a crime.
3. Tons of rapes of this sort (date rape) are not reported. It has very long lasting impact on many women, often causing serious depression even to the point of suicide attempts months or years later. She must get professional counseling.
4. She may be pissed off at you and yell at you...but 5 years from now she'll be glad you did the right thing.
5. Next time it happens, it's partly your fault if you did nothing to deter it.

Again...call the police right now!