I touched on this topic when writing about storyboarding a long time ago, but I thought it might be helpful to your writing craft to add more detail, hence this post.
When writing mysteries, you are likely going to have lots of evidence you need to bring into your story. There will likely be evidence that points to the actual criminal, to the someone whom you want readers to wonder about (the decoy), and perhaps to others unrelated to the crime. To keep track of this evidence and make sure they got into my story, I developed a system.
First, I drafted one- or two-line summaries of each of my planned chapters. I then printed them out, cut them apart, and pasted them to a piece of foam core board with enough space to insert small sticky notes between them.
Next, I wrote my bits of evidence on different colored small sticky notes, using one color for the real killer, one color for the decoy, and one for others. Then, I stuck the notes underneath the chapter descriptions into which I wanted to include the evidence.
As I wrote the chapters, I kept the board in front of me to keep on track and make sure I included the evidence I needed. Using the sticky notes allowed me to rearrange them if I changed my mind.