1. Dieters bok is based primarily on three source groups: Karin Bergman's diaries and ”thought books”, Dieter's diaries and the author's interviews with those involved, mainly with Dieter himself.
  2. A large part of the other source material consists of the letter collections in the Calwagen-Bergman family archives in the National Archives, Riksarkivet.

  3. Among other things, there is the extensive correspondence within the family, including Dieter's letters to Karin and Erik Bergman in the 1950s and until Karin’s death in 1966.

  4. Karin Bergman's ”thought books” have sometimes been called her ”secret diary”, but that's not a correct description. The ”thought books” are a couple of exercise books, filled with non-periodical notes, not always dated. One can find letter transcripts and thoughts about religion but also about family members.

  5. One of the most unique experiences in the work with this book has been to study the same chain of events depicted closely by the two protagonists of the book - Karin and Dieter - in their respective diaries.

 
The Sources