IMAGINE this: an 80-year-old Dowager Duchess is found dead in unexplained circumstances in the same house where, 40 years earlier, her children’s nanny was allegedly bludgeoned to death by the Duchess’s mysteriously disappeared, aristocratic husband. To add grist to this murder-mystery mill, the raffish, old Etonian husband is assumed to have murdered the nanny in a case of mistaken identity, believing her to be his wife (in the grim, dim light of their basement, the two women were remarkably similar in stature and appearance).

His grisly plan, so the story goes, was to do away with his wife to help pay off huge gambling debts in an attempt to restore the family fortune he’d squandered in London casinos. Having realised – to his horror – that he’s killed the wrong woman, he proceeds to attempt to murder the "right" woman (his duchess wife) with the same deadly piece of lead piping used on the nanny only minutes before.

The plucky duchess manages to escape and runs to a local pub for help. Fortunately, she lives to tell the tale but the murderous husband makes haste his escape and is never seen again.

Sounds like an outline plot for a classic crime drama. This is not fiction, nor is it proven fact, but it is what is generally believed to be the true-crime narrative true-crime narrative of the murder in 1974 of the Lucan family nanny, Sandra Rivett, by Lord "Lucky" Lucan, and his attempted dispatch of his wife, Veronica. Lucan’s disappearance has been an enduring source of speculation, films, documentaries and literature (not to mention jokes) since he vanished hours after the murder of Sandra Rivett.

With the news of Lady Veronica Lucan’s death last week (as yet unexplained, but not thought to be suspicious) there’s been a predictable rekindling of theories and wild imaginings about Lucan’s subsequent fate. Four decades on, the mystery remains unsolved but the intrigue surrounding the story is as potent as ever.

Our appetite for true-life crime stories is growing exponentially. Over the last few years, the pulling power of documentaries – such as Making A Murderer (Netflix), BBC’s Storyville series, Death On The Staircase and the universally acclaimed podcast Serial (by Sarah Koenig and Julie Snyder) – is itself something of a mystery that raises some uncomfortable questions. Why, for example, are we so obsessed with real-life crimes, and, with murder in particular? And why is it that the more gruesome and bizarre the murder, the more gripped we are by the story?

Just as murderers and the reasons they kill are complex and multifaceted, so too are our motivations for wanting to devour every intricate detail of their crimes, no matter how mundane or depraved. Real-life crime TV is a hugely popular and compulsive genre, with whole channels dedicated to wraparound, 24-hour denouement of the how and why of the dark side of human nature.

Interestingly, women are much more likely to become frequent viewers than men. This may stem from the "forewarned is forearmed" mentality of some female viewers who believe they could prevent a random attack by being familiar with the psychology and modus operandi of serial killers and rapists, thus enabling them to outsmart their hypothetical slayer. But that cannot be the only reason why the dissection of these real-life atrocities make such compelling viewing.

One theory is that we get hooked in by the incomprehensibility of murder and serial killings – often enacted on total strangers, not previously known by the attacker. The killer’s capacity to transgress social and moral norms can assign a quasi-enigmatic quality to their persona: they look like us, they act like us but, essentially, they are alien to us (this is particularly the case with serial killers such as Ted Bundy, Jeffrey Dahmer, Fred and Rose West).

Schadenfreude is another motivating ingredient that allows us to ingest the goriest of details: it’s the secret shame we experience when we feel glad that someone else is the victim while we lie safely tucked up in bed. Darker than this, though, is perhaps the unconscious, though perverse pride we may take in not committing murder ourselves (no matter how mad or bad we may feel).

Perhaps at its simplest, binge-watching true-crime TV is a form of guilty pleasure: we know we shouldn’t, but we do it anyway. The extreme and ghoulish nature of the content can be a bit like binge-eating a party pack of crisps and a giant bar of chocolate, leaving us feeling disgusted with ourselves as we survey the empty wrappers lying on the floor beside our bed.

Lots of calories and carbohydrate spikes, but no real nourishment to be had.