If we're to listen to the so-called expert profilers, it's probably a guns & ammo magazine. If we listen to a lot of the common sense analysis here, it's probably the Koran
When I heard about the book, a few things came to mind. What was the book McVey had (can't recall the title), Qu'ran, Guns & Ammo (because the profilers and posters keep mentioning it) and for some reason Catcher in the Rye (because of Hinkley).