Rest assured that investigators generally know what they are doing and have experience looking for any red flags to determine guilt or innocence.
I was accused of rape in the workplace by a patient with dementia. It was incredibly stressful and scary but I did everything my employer told me to do and let the investigators do their job and I was able to go back to work the following week.
Sometimes the system fails but chances are your friend will either get the punishment he deserves or get his name cleared.
It depends. I think that the investigators probably will find out whether he did it or not. But when it comes to his name getting cleared, there's a lot of other things that affect that. I mean, he's already got people calling him a "sick fuck" even though they probably know nothing about the case except what the papers or news say. You may have some people apologize, and may still have some who will always think you did it, even if it was proven other-wise. And this will still stain his record, most likely...
But it could always turn out differently. Either way, I hope everything works out the best it can. It's a shitty situation for all involved...