Kammala jumla mai zuwa: Bayan karshen yakin, Koehl ya yi suna ga kansa don bincikensa game da National Socialism, musamman na nazarin Heinrich Himmler a matsayin Kwamishinan Reich don Ƙaddamar da Ƙasar Jamusanci, da kuma aikin farko a kan Nazi Jamus a lokacin yakin duniya na biyu.
Mamayar Poland (1939<unk>1945). Koehl ya kirkiro kalmar "neofeudalism" don halayyar mulkin gurguzu na kasa, kuma ya kammala lissafin tarihin SS a shekarar 1983.