I love the idea of piecing together a puzzle, first of all. Showing the thought processes of a detective or someone, even a regular person, must go through to solve a mystery/problem, creates a feeling of comradeship between the main character and the reader. I have felt this connection many times with various characters and most of the best stories have some aspect of mystery to them, even if the story itself is not classified as a mystery. It could be the character figuring out why their emotional make-up leads them down destructive paths, or why someone killed another person (usually because there's no other way to solve the conflict), or why they moved to a certain part of the world. The revelations of these decisions create amazing situations. There is something special about murder though. It's sinister, dangerous, final, and hopefully not part of everyday life for most people. A special circumstance that pushes people to pursue a solution that otherwise they might ignore or push off for another day. That's the crux of murder mysteries and cop stories, especially those of the homicide detective kind. The gravity inherent whenever someone is willing to kill another human being is undeniable. A page-turner of the highest order.