One thing that might make it unique is the perspective it takes. If it focuses on the psychological state of the murderer or the victim in a new way, that would set it apart. Also, the details that are included from the real - life events, like specific conversations or small details at the crime scene, could make it stand out. It might also be unique in how it portrays the aftermath of the murder, such as how the community reacted or how the legal process played out.
One possible theme could be justice. Since it's about a murder, the pursuit of justice for the victim is likely a central aspect. Another theme might be human nature, exploring what drives a person to commit such a heinous act.