Proof that Kavanaugh is innocent.

I thought we were past this?

The FBI found him to be innocent.

Someone's innocence in the absolute sense cannot be "proven", unless an absolutely irrefutable evidence is shown that when (if) the crime was committed, they were not in the location where it happened - and such a proof is extremely rare, and definitely cannot be found for the claim on the events many decades old.

This is one (but not the only one) of the reasons why we have the concept of presumption of innocence. Whenever someone is accused of something, we assume that they are innocent, and it is the duty of the accusation to demonstrate the guilt. If the guilt has not been demonstrated, then, regardless of whether it actually has taken place or not, the suspect is found innocent.

So, in a way, the proof of Kavanaugh's innocence is the fact that no evidence of the contrary has been demonstrated. It is not the proof of his innocence in the absolute sense (that he did not sexually assault the woman in question), but it is the proof of his innocence in the legal sense (that he has not been found guilty of the crime).