Theoretically. Practically, that legal theory is just a smokescreen for the willingness of the government to overlook any misdeeds by the secret services. Prosecutors and courts got the hint and didn't investigate any further. However, if you are a non-state-sponsored criminal, of course you will be prosecuted. "Qvod licet iovi, non licet bovi" is a very important legal principle ;)

Also, later on, the government just legalized what the BND was doing, thereby invalidating any future attempt at prosecution for that past crime against the BND. Yet still maintaining the illegality for everyone else.