my guess as far as the date rape drug goes, is that she probably tested for something that the prosecution will try to use as evidence of an overall crime, but not as crime in itself, because of the lack of evidence..
Nifong has been playing fast and loose. He's had those tox reports for awhile, even if he says he doesn't. If there was a date-rape drug in her system, he'd have charged them. There's something very fishy about all of Nifong's moves. I think he's covering up his lack of evidence but intimating that he actually has some. The other possibility is that she wouldn't give consent for tox and BAC tests.