Not a big revelation, but it came to my mind as maybe to some discussion:
Mageau said quite conflicting things in my opinion (probably not a big revelation actually)
1.That they thought it was a policeman and they started looking for papers when he was closing in
2.Later during the zodiac movie 2007 documentary he revealed that darlene said his name was richard and that he was jealous or something (you can correct me on the details if I'm wrong, you probably all get the picture here)
So unless both are true and Darlene knew a cop named richard and this was a cop (doubt it, not my point here), if Darlene knew the killer, especially as a jealous boyfriend or ex-boyfriend then she would unlikely play on and comply with looking papers as Michael Mageau told her because what would be the reason to show her papers to a jealous boyfriend? Or why would she play that game with Mike? I think that would be plain silly of her. So I think that while compelling, the whole "darlene knew the killer" has no grounds on Michaels own testimony.
I think that even if she knew him, reacting all that she was probably having no clue and probably getting the idea from Mike that implied that this is probably a cop.