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- Biography in Dutch by OperaNederland.nl with photo.
- F. C. DeCoste, Bernard Schwartz The Holocaust's ghost: writings on art, politics, law, and education p80 2000 "Others who died in Auschwitz, often via Holland and Terezin, were Alfred Kropf, a conductor from Stettin; Magda Spiegel, a Frankfurt contralto; and composer James Simon, a student of Max Bruch."
- Peter Hugh Reed, American Record Guide, No. 16, 1949
- Dinah Shelton, Encyclopedia of genocide and crimes against humanity, 2, 2005. Quote: "However, among them are: the baritone and cantor Erhard E. Wechselmann, murdered in Auschwitz; the contralto Magda Spiegel, murdered in Auschwitz; Richard Breitenfeld, a member of the Frankfurt opera ensemble, murdered in Theresienstadt"
- Great singers, from the seventeenth century to the present day Kurt Pahlen - 1974 Ottilie Metzger-Lattermann, who before 1914 had sung in all the important opera-houses and at Bayreuth, died in Auschwitz; the baritone Richard Breitenfeld, also a Wagner lead, in Theresienstadt.