When you are writing a story, often pieces will just come together. This happens as you write or even when you are imagining how it will all happen. It happens as you begin to know your characters.
When I wrote Desert Inferno, I spent time thinking of not only the hero and heroine but also the villain. Villains are an important counterpoint to the good of the hero and heroine. This one had something occult about him without it going so far as into the metaphysical. He believed he had power through ancient Aztec rituals and sacred items. One in particular was a crystal skull which I knew had been created back then in the Mayan and Aztec cultures.
Recently I came across the following article which pretty much validates what I felt about the villain's belief he could gain power through such methods. I hadn't read it when I wrote the book but like how truths often come together even if it takes awhile. I wouldn't change the book because it says enough as it is but this is an interesting addition.