Nutshell Studies: The Barn
This letter from Mrs. Lee to Alan Moritz is one of the few discussions of her work on the Nutshell Studies and documents the meticulous details involved in their creation.
I am glad you have found the study of these cases interesting. I found myself constantly tempted to add more clues and details and am afraid I may get them "gadgety" in the process. I hope you will watch over this and stop me when I go too far. Since you and I have perpetrated these crimes ourselves we are in the unique position of being able to give complete descriptions of them even if there were no witnesses--very much in the manner of the novelist who is able to tell the inmost thoughts of his characters.
Mrs. Lee also makes it clear that the models were based on actual forensic cases--one of George Burgess Magrath's, in the example of the Barn--although the circumstances were changed to prevent identification.