What are the motifs in In the Lake of the Woods by Tim O'Brien?

Mystery is a recurring idea. The story is presented as a research effort by the author and deep into the book, he includes a footnote that outlines the reasons people will be interested. The author points out that people love a mystery. He says that people are compelled to examine unsolved cases, such as the story of Lizzie Borden who may have killed her family with an ax or the question of whether Lee Harvey Oswald acted alone in his assassination of John F. Kennedy.