Now, at this distance, I realise Venables is nearly 30. I find the confluence, if that’s the word, of his ruination and my visibility disturbing. At some level, I will always feel I could have been Venables and the more opportunity I get to make myself understood, the more it becomes obvious that he will never escape condemnation, the thing John Major called for more of in his statement at the time of the trial. I have dreams about the boys, and sometimes dream I am the person in the CCTV footage who walks past them with a shopping bag at the exact moment they abducted James. I can see the butcher’s shop where James’s mother is waiting for her change; I see the floor tiles reflecting shadows and hear the mall’s muzak bending sinister as the shoppers go about their business. I hear the echoing swimming-pool clamour of the ordinary day about to go wrong…

Late in 2007, Gerry McCann gave an interview to an American magazine and talked about the decision to publicise the eye defect. “Certainly we thought it was possible that [the publicity] could possibly hurt her or her abductor might do something to her eye . . . But in terms of marketing, it was a good ploy.”

It is this unsettling mix – of the incredibly intimate and the coolly tactical – that has made the mystery of Madeleine McCann arguably the biggest and most extraordinary child abduction story in history…

For Truman Capote the outcome of his sojourn in west Kansas was decidedly mixed. In Cold Blood, which he immodestly heralded as a new form of non-fiction novel, was received with delirious approval; Norman Mailer dubbed Perry as one of the great characters in American literature. The book earned its author more than $2m, which he used to buy homes in Manhattan, the Hamptons, Palm Springs and Switzerland. But by all accounts such heavenly success also went to his head, and contributed to his downward spiral in a haze of lavish parties, drink and drugs. He failed to write another substantial work, and died in 1984.

‘His testimony offers a compelling argument against conspiracy theories. He spent between five and seven years roaming the corridors of power like the Invisible Man, wandering into Pentagon offices, rifling through files, and he found no particular smoking gun about anything. He unearthed nothing to suggest a US involvement in 9/11, nothing to suggest a UFO cover-up. Nothing, he told me, except two things…’

He tried to explain what drew him to his computer. “When I’m talking to Cindy or you like this, face-to-face,” he said, “it’s hard for me to say what I feel.” As Tommy, however, the words came easily. And then there was Jessi. He loved her, or at least believed he loved her, though he knew he was “never going to meet her.” His plan was to “kill Tommy off” in Iraq, but Cindy intervened too soon. He nearly committed suicide because of his guilt about having lied to Jessi.

‘Consider the pace at which the story unfolds. Nobody is in control of it, which means it occasionally gets quite dull. We can’t fast forward or time-switch. We’re not invited to phone in and vote for which suspect we would like to see arrested. Key scenes and pieces of information are kept from us in a way that would defeat the point of a show like Big Brother. But we find this all the more compelling. The one nod to conventional broadcasting principles is that the ratings have mattered right from the beginning. When there was a risk that they might slump, David Beckham was drafted in to speak on the matter, thus giving the story a new boost. Most grippingly of all, we have no idea what genre of story we are watching, so have no idea how or when it might end.’

Suddenly we have to hold two entirely contradictory thoughts in our head at the same time. For the McCanns have now either suffered the cruellest fate imaginable – not only to have innocently lost their beloved daughter but also to have been publicly accused of a wicked crime – or they are guilty of the most elaborate and heinous confidence trick in history, deceitfully winning the trust and sympathy of the world’s media, a British prime minister, the wife of the American president and even the Pope, to say nothing of international public opinion. One of those statements, both of them extraordinary, describes the truth. As a senior tabloid journalist put it to me yesterday: “They’re either the victims of a horrible smear which they will never fully escape or they are cold, psychotic killers” responsible for the death of their own child.

‘Hare had his subjects watch a countdown timer. When it reached zero, they got a “harmless but painful” electric shock while an electrode taped to their fingers measured perspiration. Normal people would start sweating as the countdown proceeded, nervously anticipating the shock. Psychopaths didn’t sweat. They didn’t fear punishment — which, presumably, also holds true outside the laboratory. In Without Conscience, he quotes a psychopathic rapist explaining why he finds it hard to empathize with his victims: “They are frightened, right? But, you see, I don’t really understand it. I’ve been frightened myself, and it wasn’t unpleasant.”

In another Hare study, groups of letters were flashed to volunteers. Some of them were nonsense, some formed real words. The subject’s job was to press a button whenever he recognized a real word, while Hare recorded response time and brain activity. Non-psychopaths respond faster and display more brain activity when processing emotionally loaded words such as “rape” or “cancer” than when they see neutral words such as “tree.” With psychopaths, Hare found no difference. To them, “rape” and “tree” have the same emotional impact — none.’

‘The Catholic religion teaches us that redemption is possible, that even the greatest sinner – even someone who has tortured and killed children for the obscene pleasure of it – can be washed clean of their guilt. Evil is a noun, something like dirt inside you. But for most of us, evil is more like a verb: something you do, not something you are. This is the more modern and more terrifying view of our moral universe – because, instead of regarding Hindley as simply monstrous or aberrant, ‘possessed’, as it were, by evil, we have to start seeing her as not so very different from all of us, just someone who made different choices. She is not alien, but human. This is what humans can do, if they take the hellish road and step by step go down it.’