Ghostwriting a mystery or one of its sub-genres (police, detective, cozy, malice domestic) requires that a ghostwriter have a strong ability to foreshadow events in the plot. A crime is solved by a protagonist (a detective, police officer, or amateur sleuth) finding clues, and the challenge for a mystery writer is to inject these clues into the narrative at the right places so as not to give away the ending.
The protagonist should have a distinctive personality, whether he or she is a detective, police officer, or an average citizen whose hobby is solving crimes. And knowing where to drop in those all-important red herrings is crucial in keeping the reader a little off-balance until the case is resolved.
Mysteries are riding high in the literary marketplace, just as they are on television. It's an excellent genre to explore, and many of the top-earning writers today write police procedurals. The genre also naturally lends itself to expanding a single title into a series.
If you're an author interested in the world of suspense and who-done-its, contact me and I'll take the mystery out of how to get started.
You may also be interested in Ghostwriting a Series.