He is the author of "The Good Old Days": The Holocaust Through the Eyes of the Perpetrators and Bystanders first published in English translation in 1991.

During this period, he collaborated with Gusti Steiner, who laid the foundation for the federal German emancipatory movement of the disabled at that time.

The explanation states that Klee's works "are suitable to support civil freedom, moral and intellectual courage, and to give important impetus to current awareness."

[3] In 2003, he wrote an article criticizing the omission of Nazi activity in the career details of those mentioned in the Deutsche Biographische Enzyklopädie ("German Biographical Encyclopedia")[4] or his description of the relationship of German artists to the Nazi extermination camps in German-occupied Poland.

[5] Contemporary author Karl-Heinz Janßen wrote on 27 February 1987 about Klee, "Contemporary historical research ignores this subject [of medical crimes during the Nazi period]; [...] if it were not for the free-lance journalist, Ernst Klee, who went to the effort of reading thousands of case files and rummaging through archives of institutions, almost nothing would be known today about one of the most horrible atrocities of this century."