During the night of 24 November 1987, the Stasi and a public prosecutor broke into the premises of the East Berlin Zion Church. They were hoping to catch staff from the Environmental Library, which was based there, printing the illegal magazine grenzfall ("Borderline Case/Fall of the Border"). But the staff were actually printing the semi-legal Umweltblätter ("Environment Letters"), a church newsletter that the state was forced to tolerate. Although the secret police had no evidence of a crime, they still confiscated the machines and arrested all those present.
The GDR government had underestimated the opposition networks, however. They published a joint protest letter the very next morning, which went all around the world via the West German media. Western politicians demanded the prisoners' release. Public intercession prayers and solidarity campaigns for them were held across the GDR, with a vigil set up in the Zion Church in East Berlin. The prisoners were released in the face of this widespread public protest. This was the SED's greatest defeat against the opposition before the end of the East German state.