When I wrote my first mystery, A Matter of Taste, I had pretty much everything outlined. Even if I didn’t have certain plot points actually written down on paper, I at least had most of the story in my head before putting fingers to keyboard. Being new to the genre, I figured it would be best to have all my clues, suspects and red herrings organized and mapped out in advance.
red, but not a herring
In writing circles, this is called being a “plotter.” The other alternative is a “pantser”—as in seat-of-the-pants—where you just sit down and write without much of an outline.