One of the biggest challenges for beginning mystery writers is how to present the villain and still keep that character hidden until the sleuth reveals them at the end. You want to share enough of the villain so your reader feels they could have guessed. On the other hand, you don’t want to give away to much in the story so your reader guesses the villain before the end.
To keep your villain hidden as the perpetrator until the end you need to create a discipline in your story. The bits you share about your villain are like any other clues.
Chris The Story Reading Ape's Blog 