Legit question....someone makes a claim, no evidence, no witnesses, no proof, decades after the fact...hiw do you even start to investigate?
Typically you would interview the accused and accuser to lock down the story. Since he is saying it never happened you won't get much from him. From her, you may or may not get the home it happened in. If the floorplan fits what she described that adds credibility. If the owners can confirm that room had a stereo that could be turned up, another straw. Not saying after these many years that will happen but it could. They'll work on finding out if they can determine other people at the party. Who did she hang out with at the time, did she go there alone, that kind of stuff.
Mark Judge, his not recalling it could be that it didn't happen, could be he binge drank as he says he was prone to do and blacked out.
At the end of the day, I don't think it's possible to prove it happened or disprove it happened. There are things they could find that would lend credibility to one side of the story or the other and report the findings without drawing a conclusion.
Again, I can get past the "I was 17 and drunk" argument. I've never done that but lets say he did. It was a bad thing. It obviously caused her a lot of emotional strife. But if there is nothing in his record or history to indicate a pattern or even a repeat of this, then for me, I would not disqualify him for it. However if it turns out to be likely true, and he chose to deny it rather than own it, that would speak to current integrity and is a different story. My best guess is due to the time that has passed, people who may have known anything about it either dying, moving away and not having contact, it will turn out to be inconclusive. But I do think it ought to be looked into.