Fayed snr has reason to detest the British establishment, so it's not altogether surprising that in his grief he convinced himself that the ruling class would go to any lengths to stop the people's princess and mother of a future king marrying the playboy son of an Arab arriviste.
But this new "scope" - as the Yard calls it - was prompted by a two-year-old letter from the parents of a former SAS man's ex-wife. It seems he made the claim as part of a campaign of intimidation against his estranged wife and in-laws, along the lines of "we knocked off Di and got away with it, so getting rid of you lot would be a doddle".
The man, who served in Iraq and Afghanistan, was discharged from the army after being convicted of illegal possession of firearms. It seems clear that he has post-traumatic stress disorder, the symptoms of which include delusions and paranoia.
(It's estimated that there are at least 200,000 combat veterans in US jails, half of them for violent offences. In 2009 there were more vets in UK jails than there were British soldiers in Afghanistan. Another reason to think very carefully before sending young men and women to war.)
Diana and Dodi weren't wearing seatbelts. Their chauffeur was three times over the drink-drive limit and taking anti-depressants. The inquest, which was preceded by a three-year Scotland Yard investigation and overseen by a jury, concluded their deaths were an accident, as did a separate French investigation.
It's one thing to claim a British conspiracy, but to believe Britain and France could collude in such an exercise when they've hardly agreed on anything for 900 years suggests a perilous detachment from reality.
If Scotland Yard feels the public interest requires this absurd claim to be investigated, why couldn't it have done so quietly, behind the scenes, which is how the police and security services normally prefer to operate? What does a public announcement achieve apart from upsetting Diana's family and over-stimulating the already irrational and credulous?
American crime novelist, Elmore Leonard, who died this week was one of the few writers to achieve the double of critical acclaim and commercial success.
Lauded as a literary genius by highbrow writers such as Saul Bellow and Martin Amis and lionised by Hollywood heavyweights like Quentin Tarantino, Leonard also had the less heady but more to the point validation of being a constant presence on the bestseller lists.
However it's hard to believe that anything in his extensive output gave him greater pleasure than his 10 Rules for Writing, published to a reverential reception in 2010. After his death the bullet point version was being pored over as if it had been discovered on a stone tablet on Mt Sinai.
As Leonard was no doubt well aware, creative writing rules are a contradiction in terms. And given the dark sense of humour so evident in his work, it must have amused him no end that his rules were taken so seriously.
Some seem like advice for people who'd have trouble crafting a note to remind them to put out the rubbish: "Keep exclamation marks under control." Some seem like advice for writers who'd really rather be doing something else: "Avoid detailed descriptions of characters; don't go into great detail describing places and things."
Leonard was a master of the crime caper, an unerring chronicler of the American underclass and, in his own way, a consummate stylist. He, Raymond Chandler and Ross Macdonald are the great triumvirate of 20th century American crime writing.
Macdonald said Chandler "wrote like a slumming angel and invested the sun-blinded streets of Los Angeles with a romantic presence".
You don't do that by following someone else's rules.
