Because he knows, or at least because his author knows, that a scene of crime officer would soon arrive. The SOCO and a horde of uniformed cops would take control. The house would be declared a crime scene, and zoned off. Nothing could be moved or even touched. Photographers would record in minute detail the place where the body was found, and everywhere else of potential interest. A doctor or a pathologist would have to attend. Witnesses and dependents would be separated from each other for individual questioning.

Many readers will have a sceptical view of the efficiency of the police, especially in times of budget cutbacks, but in fact a modern force has a huge range of technical and scientific means of investigation. In recent years the work of identifying a murderer has been transformed by forensic science.

None of this is any good to a crime novelist. The crime must not be solved by experts, working out of sight in some laboratory. He does not want a helicopter with night-vision cameras to search the grounds. Instead, the bereaved family and their servants must gather, partly to reflect on the evil ways of the deceased, partly to accuse each other of complicity. They will each declare their own innocence, settle old scores, establish alibis, reveal the existence of hitherto secret promises or documents. There will be talk of sinister strangers moving silently through the shadows in the grounds.

Meanwhile, the sleuth, amateur or professional, will lurk quietly in the background, taking notes, interrogating suspects, studying railway timetables and the like.

The existence of a police investigation would ruin this.

Although modern writers have mostly dispensed with the template, elaborating and sophisticating it, the essence remains: a professional investigation does not make a compelling plot. The emphasis can shift to the police officer in charge: his or her weaknesses or strengths allowed to dominate the story. Details of police work can themselves make fascinating fiction of a different kind. Or the possibility of police intervention is removed altogether: a remote location for the scene of murder, landslides or snowdrifts preventing access, some social emergency tying up police resources, and so on.

The classic crime story was always a kind of artifice, and no reader or writer thought otherwise. But all thrillers, made as fiction, require special conditions for the story to work. Crime writers create self-contained worlds, or at least they carefully contrive a special area of the world that only seems realistic, where what we know about the reality of murder and its detection is set aside, forgotten. When we write crime we think little of real crime.