My understanding is that these drugs were being shipped from legitamate pharmacies (not some warehouse or personal residence) and that Fedex has a metric ton of legitamate prescription drug shipping business.

So they are faced with the challenge of trying to identify which packages (of which they don't know the details of the contents) are legal and illegal. Quite difficult, so they ask the gov't to tell them which ones are the bad actors and the gov't refuses.

Good for them for fighting the charges.