As I read your posting over the last weekend, the image that came to mind is that of a criminal court room and you are the jury with your h on the stand and the prosecuter is has brought up your H's alibi is that he did nothing...
"Were you with anyone that can confirm you did nothing?"
"No"
Well there's the OW, but we all know her credibility is worthless to the jury!!!
"Do you have any evidence that can prove you did nothing?"
"No"
After all, how can something exist that will prove that nothing existed?
... and that is my point here LL ... you are looking for evidence to exist that proves your H is telling the truth about a PA that didn't happen. Your H is caught up in a catch 22. If it didn't happen, then how can H produce evidence that he is telling the truth that nothing happened?
He can't, he has to put his fate in the jury's hands. That's why we have a judicial system that works on the premise of "being innocent until proven guilty", because evidence doesn't always exist to prove innocence. (... and remember we're only talking about innocence on the single charge of having a PA.)
So ... how will the jury rule? (... and remeber once the jury reaches a verdict, there's no retrial.