Frankly, they needed a break. In five novels, I'd put them through hell. I didn't think they, or anyone really, could handle another emotionally, physically, and psychologically damaging case within the period of another year. So I gave them a breather. Oh, God, I don't know.
Biographical influences are often so hard to put a finger on.
And, to a large extent, I don't want to understand too much about what fuels my writing. I try to hold onto a measure of respect for my creative demons, if you will. To over-analyze them could render them impotent. What little I do understand about my obsessions is that I'm attracted to classical tragedy as a form. As for future novels, I'd like to expand a bit thematically.