Something along those lines CB. My thoughts exactly, but I am 99% sure the victim will never report it. I have no other evidence than what I have heard from the victim, which they could always refute saying.

@KC- then you don't have evidence unfortunately. Can you verify her/his claims?

No evidence, I never said I did. I know who did it. And I know who else knows. I have zero first hand knowledge.

But people with that knowledge aren't/haven't talked.

@KC- I think its best you talk it over with the victim. see if they want to come forward and just stand by their side

If you did not witness the crime, then you shouldn't report it without the victim's consent.

Unfortunately, that seems my only option.

The victim's consent is necessary to press charges.

And so a guilty man walks free...

Most rapes are unreported and most women refuse to report them. I'd kill the bastard myself if I were you but prison is unpleasant. If someone rapes once they will do it again until they are stopped. It's not a one time thing.

I've come close to breaking some bones...

Try talking to the victim and convincing them that unless they do something then the perpetrator will get away with doing it to countless others. Also there is a statute of limitations on such accusations in most states I believe

Kill him

Vigilante justice is illegal for a reason. I sympathize with the sentiment, but consider the possibility that the "criminal" in question is innocent. I'm sure Cyrus has reason to trust his friend, and I'm not calling into question his judgement specifically, but if we're morally comfortable with him making that call, then we're heading down a slippery slope.

Making that call unilaterally*, I should clarify. At some level any form of exacting justice involves people "making that call." I happen to think it better for that power not to rest in the hands of any one individual.

you should report it. not reporting is a crime too. you could report it to gunfighter, if fear for police questioning of the victim. Try to speak to a female officer (you can explicitly ask for this).

as you live in the US, do you live in a state were only forcible rape is a crime? you should make sure to prove this too.

as an alternative: watch/read "Gone Girl" and put into a similar scheme. Maybe you'll get the victim on board as well. (I personally would go with my first recommendation)

Is there anything more you can tell us? from the gist of it, maybe have a sit down with the victim and talk through the options

You know neither that there was a crime nor who did it if there was. You have nothing to report. The only choice you have is whether or not to betray the victim's trust in you for no benefit whatsoever. Clearly you should not.

@TrPrado It is always to report a crime even if you are not the victim. Depending on where you live the victim doesn't have to be the one to press charges – depending on the crime the district attorney can press charges too even without the victim's consent. Unfortunately, in rape cases most countries defer the charge to the victim instead of taking up their cases on their own.

"it is always possible to report a crime" I meant.

If the perpetrator is truly guilty they will usually have some character weaknesses you can exploit. Help them get addicted to a dangerous narcotic by subsidising the first romance. Once they are well hooked cut off your subsidy and any contact. The rest should take care of itself.

Caution: Some might advise this is morally questionable. Pro tip: Watch out for unintended consequences!

I'm with the crowd here: you don't have anything to report, nor any right to.

The underreporting of sexual violence is tragic. But it's not your tragedy, it's your friend's tragedy. Support the victim best you can.

@KC.
You do not know that a crime was committed. All you know is that someone claims to be the victim of that crime and has named the alleged culprit. You were not a witness and have nothing to add to the evidence.
In such circumstances it would be arrogant to take upon yourself the responsibility of reporting the alleged crime. The alleged victim may have re-framed his/her memories of the events or may have no wish to put him/herself through the trauma of recounting the story to a complete stranger and then later, possibly, to a whole roomful of strangers, at least one of whom will have as his/her sole purpose to undermine the credibility of the victim.
The chances of securing a conviction after even a short delay are low. Unless the victim suspects that the perpetrator's behaviour is part of a pattern of behaviour about which s/he may be one of several complainants, reporting the crime is likely only to increase his/her sense of powerlessness.