Horst Jänichen was born in 1931 in Berlin. In 1946, he was arrested by the Soviet Secret Police, under false accusations that he was a member of the forbidden "Werewolf" group.
He spent two years in Soviet special camps in Berlin-Hohenschönhausen and Sachsenhausen. He then joined the "Troop Against Inhumanity," which campaigned against the SED-dictatorship. In 1950, the East German State Security Police arrested and sentenced him to eight years in prison. In 1959, following his discharge, Jänichen fled to West Berlin.