The author's birth name was Alan Alexander Milne, but his pen name used only the initials A. A. Milne. He eventually won worldwide acclaim for his renowned youth-oriented stories about Winnie-the-Pooh. However, he tried something different a few years before that, a story based on parental devotion. He explained his reason for that in his preface:

TO JOHN VINE MILNE, my dear Father,

Like all really nice people, you have a weakness for detective stories, and feel that there are not enough of them. So, after all that you have done for me, the least that I can do for you is to write you one. Here it is, with more gratitude and affection than I can well put down here. —Alan

How's that for an introduction to a "whodunit"? Just listen to what he wrote.