In my opinion, it's the same issue that arises with a search warrant or a wiretap warrant. Indeed--and this is the actual wording in the Code--no detailed information is to be disclosed regarding the reasons for the search or the wiretapping.
In fact, counsel for the person who is the subject of the search doesn't even know about it until the search has already been carried out. Counsel for such an individual, just as for someone subject to wiretapping, does not know, unless he or she has been advised in another fashion, that his phone is being tapped until 90 days or some time after the wiretapping has already been carried out. The person doesn't know that his phone is being tapped and is unaware of the reasons why it's being done; they may be secret. It goes before a judge and the judge is the one who decides whether or not the wiretapping will be authorized. If the application is dismissed, no one knows why it was dismissed, and no one knows the reasons that were given.