The 1966 murder of Dr Helen Davidson near Amersham, Buckinghamshire, is the subject of Monica Weller’s cold case investigation. To give you half the answer you’re looking for: yes, she solved the case. And no, no spoilers here.

What Monica Weller also discovered, perhaps to her own surprise, was the extent to which a close-knit market town would close ranks over the mists of a local wood to bury the case. Surprising because New Scotland Yard sent a senior policeman to ‘help’ with the enquiry. Even he couldn’t get to the bottom of anything, perhaps because he was pressured by the Thames Valley Chief Constable, who himself knew the victim well and had helped to cover up a car accident which Dr Davidson had caused some years earlier. Or perhaps because he jumped to fairly predictable, unimaginative conclusions in the days before DNA fingerprinting had arrived.

What surprises me, having read this fascinating and persuasive account, is that the local papers continue to request witnesses and information on the major anniversaries of Dr Davidson’s murder. Why? Because it is beyond all doubt who killed Dr Davidson. And why do those copies of the Bucks Free Press regularly go missing from their archive, even as recently as 2006?

What I am finding, and the key takeaway from some of my recent reading, is that there is a wide gap between what might seem to you, or me, blindingly obvious, and something that can be proved beyond a reasonable doubt. This is something the police are carefully trained on: the difference between the sheer blinding obvious, and the necessity of finding the evidence to prove it to a jury. And before the jury sees it, the CPS has to agree as well.

There is hope, however. Because what I am also learning very quickly is that anyone with a profession, someone whose livelihood is somehow linked to murder and other serious crimes, is involved in those crimes, however obliquely. An unsolved case is a badge of failure. How many people do you know who, if faced with disciplinary action, the loss of a job, or the embarrassment within their own social circle, would proudly stand up to admit failure, and damn the torpedoes? Not many. There is hope for us, for the ‘unprofessional’ amateurs, the armchair enthusiasts. We are free to pursue the truth without fear, without a disciplinary committee ready to strike.

And look out for this in your own investigations: a case from the 1960s or 1970s involving members of society such as doctors, surgeons, judges, the clergy, an accountant, perhaps, or a solicitor… such cases are more likely to be ‘thrown’ by the old boy’s network. Incredibly, this case of a murder in sleepy Amersham is even tangentially linked to Kim Philby, the most notorious of the Cambridge Five KGB spy ring. Where the ‘establishment’ treads, there is always the possibility of a major cover-up. Just ask Bruce Robinson about Jack The Ripper. More on that story another time.