Polt muss weinen (2001)

The property speculator Albert Hahn is found dead in his cellar. He died of fermentation-gas poisoning. The doctor in charge assumes it was an accident. But Polt, the responsible gendarmerie inspector, knows that the deceased was hated in the community. He suspects that the killer wanted the death to look like an accident. Many of the winegrowers would have had a motive. After lengthy investigations in the wine cellars, Polt discovers that all the cellars are connected to one another by holes. The feeling that Hahn’s death was murder—a suspicion that had come over Polt from the very beginning—will not leave him. As he sits drinking wine with his friends, they confess that they committed the act together and poisoned Hahn with fermentation gas. One of the friends wants to take the blame, since two of them are married and have children. He then does indeed commit suicide, leaving behind a confession to that effect.