Hmm. Since the Dramatica Critical Flaw only applies to MC and IC, I think you could look at items like:
OS Solution (if defeating the villain helps resolve the OS) … although this wouldn’t really tell you what the evidence is, but could give you ideas on how the MC goes about getting it. (e.g. through Proaction, or Determination, or Temptation)
Requirements or Prerequisites might give you some ideas
The applicable OS signpost
MC Unique Ability – maybe they use this to find/get the evidence
Is it possible the evidence isn’t found, but made up (like fake evidence)?
When I used the methods you described, I found that our MC is basically going through those methods. This is a Failure/Bad book (a noir), so even though she finds the evidence against this villain, it doesn’t solve her original goal. It actually makes things worse for her personal life, particularly her marriage (long story).
What I did was to go into the character tools in Dramatica, to see what traits fit the villain. Once I had a list (he’s quite complex), I looked at the list to see what mistakes he might make, particularly ones with paper trails.
Edited to add: I also looked at what others have already said about him so far in a negative sense (weaknesses), to see what if anything I might exploit.
So it’s a start. If I figure anything else out, I’ll let you know.
This brought to mind when Dramatica hit the world running with TCM channel pouring out all the old great films for affordable non-interrupted viewing. I was overwhelmed by my discovery of the contagonist as a real objective story tool that had existed in the history of storytelling, It was always fascinating to see how that character really did have his/her own agenda using temptation and hinder. Perhaps, that would be a possibility.