With its decision of 20.01.2021 (C-619/19), the European Court of Justice followed the argumentation of the state of Baden-Württemberg, represented by Dr. Torsten Gerhard, and significantly strengthened the position of the state in connection with the obligation to disclose environmental information. The ECJ held that an authority may invoke the protection of internal communications even after the conclusion of an administrative procedure and does not necessarily have to disclose them to citizens. In doing so, the ECJ assumes a very broad understanding of the term "internal communications". Whether the conditions for a claim to access to environmental information are met must therefore be decided in each individual case.
A final decision on the citizen's action for access to documents relating to the investigative committee on "Stuttgart 21" and the conciliation proceedings has therefore not yet been reached: The Federal Administrative Court and, if necessary, the Administrative Court of Baden-Württemberg must now decide how the abstract criteria laid down by the ECJ in its landmark decision are to be applied in the specific case.
A SWR report with a statement by Torsten Gerhard can be found here (from minute 3.55).
You can find the report of the Stuttgarter Zeitung here.