Actually, the issue goes beyond release of the black box and other crash data. The real subject is "who has authority over air operations?"
Granting political, headline-grubbing local prosecutors the ability to charge people is an invitation to chaos, where local cops and prosecutors can grab headlines while having absolutely no expertise in the matter at hand.
In some countries, the ability to govern air operations and enforce air law is not granted below the national government level. In the US, for example, locals have no jurisdiction, only the FAA can enforce aviation law. While they can be bureaucratic, at least the FAA has expertise and familiarity with the law. Also, the crash site and data can be impounded by the National Transportation Safety Board, which has full authority over crash investigation. The NTSB will not permit its conclusions to be used in any court, by Federal Law. The data they gather is public record, and can be had by almost anyone.
As Flying Lawyer so rightly describes, protecting the quest for truth and the ability to fix the system is paramount. The process must, in the end, make the next accident less likely to happen or the process is broken.