As to NP's demeanor yesterday, I think part of it is that there's an issue with FD paying him, IMO. It's not necessarily that FD's (err... GF's?) money has run out, but he might realize that LE is watching his financial moves, as well. "I promise I'll pay you more when I can get access to the funds..."
As to FD's smiling/smirking, he did it much less, but did start to smile when the female reporter came up to his right side, then seemed to catch himself.
Perhaps he's finally been told that smiling after the mother of your 5 children is supposedly "missing" is not a good look, and makes him look all the more guilty?
Regarding her medical bill/paperwork, he can't use it as evidence if he doesn't show the actual bill, can he? Then he would need to explain where he got it; I don't see how a jury can use that info without the actual document.
Edit:
Happy birthday, @enelram!