The State Security for East Germany were known as the Stasi. East Germans feared the Stasi with good reason. They terrorized the country during the cold war. In Dead Wrong in Gorlitz Park, German PI Graf (Duke) Andreas von Reinecker goes through the Stasi files of his client’s mother looking for clues to help locate the older woman.
When the Berlin wall came down, the Stasi tried to destroy the files of information they had collected on their own citizens, but they didn’t succeed. After reunification of the two Germanies into one country, the new German government made the decision to allow citizens to read their Stasi files. East German learned that children, spouses and friends they trusted had informed on them to the Stasi.
The International Institute for Journalism of GIZ provided a good description of the Stasi and the archives containing the files the Stasi collected in the blog article, “Dealing with the past: the Stasi archives in Berlin” by Bukola Adebayo.