Once granted the status of political refugee, Mandl moved to Cologne, where he became the private secretary of Heinrich Böll, the recipient of the 1972 Nobel Prize for Literature.

This incident is documented in Mandl's autobiography, Durst, Musik, Geheime Dienste[7] published in Germany in 1995 and in a Bavarian television film directed by Gloria de Siano.

In later years, Mandl produced and edited cultural broadcasts that were transmitted to Communist Eastern Europe by the West German radio station Deutsche Welle in Cologne.

During the last decades of his life, Mandl was a very active as a contemporary witness to the musical scene in the Terezin (Theresienstadt) ghetto; he had played the violin in the camp orchestra in 1943/44 under the batons of Karel Ančerl and Carlo Sigmund Taube.

Mandl was a tireless contemporary witness to the horrors of life under totalitarian regimes and particularly to the Holocaust, traveling throughout Europe and North America to deliver his message.

The central theme of Mandl’s literary work is the battle of the individual against the sophisticated instruments of totalitarian oppression: secret services, isolation, psychological torture, brainwashing, incarceration, starvation, the debilitating effects of the "daily grind" in the most difficult of circumstances.

As in works by Edgar Allan Poe, Aldous Huxley, Franz Kafka and George Orwell, Mandl's protagonists, armed only with their reason, stand alone against all the sophisticated torture arts of their seemingly omnipotent opponents.

Other unpublished stories, dramas and presentations with philosophical and political themes are contained in Mandl’s bequest to the archives of the Moses Mendelssohn Academy in Halberstadt, Germany.