VIENNA - I first met Oswald LeWinter in an Austrian prison in the year 2000. It was the first time I had visited a penitentiary and the first time I had ever met someone like Oswald.

 LeWinter was completing a two-year prison sentence for attempting to defraud Mohamed Al Fayed. He had been arrested in Vienna as he tried to sell the Harrods boss what he said were secret CIA documents proving that Al Fayed’s son Dodi and Diana, Princess of Wales, had been killed on the orders of Britain’s foreign intelligence service.

 This was perhaps the most spectacular imbroglio in a long and controversial career.

 LeWinter had written to me saying he had received a copy of my book, Puppetmasters, which he had read with great interest.

 “There are a number of issues you write about, some errors, some things you could not have known,” he wrote. “I am prepared to meet with you if you wish to clear up some important matters.”

 In the letter LeWinter referred to an interview he had given to the BBC in which he “spoke about a meeting in Rome at which I was present with [Italian military intelligence chief General Giuseppe] Santovito and [Henry] Kissinger in which Moro’s fate was sealed. I had warned Moro that he would never be allowed to implement his political plans.”

 LeWinter said his interest in speaking to me also had a personal component. “I am impressed with your investigative abilities and have a perhaps interesting project to propose to you.”

 LeWinter’s project was a biography of a self-confessed disinformation specialist: himself. Following his release I travelled to Lisbon and talked to him at some length, but I never wrote the book.

 Oswald was forthcoming on subjects I knew little about, providing me with details that would be difficult or impossible to check, but surprisingly cagey when it came to my own specialities.

 It wasn’t clear whether the real purpose of the book was to celebrate his own achievements or demolish mine.

 Another journalist frustrated by his disinformation antics described how he appeared when they met for a confrontational TV interview about his efforts to muddy the October Surprise story: “LeWinter looked like an out-of-shape fireplug. His face was bloated, and his tired eyes were those of a man who had fallen woefully short of his potential in life.”

 On that occasion LeWinter told Robert Parry how he had undermined the work of the investigative author Barbara Honegger on the alleged plot to delay the release of US hostages in Iran in order to favour the election of Ronald Reagan. It involved using tactics that would recur throughout his career.

 “I managed to pass on some information to her which had factual elements in it, but also elements that with a little bit of digging could be discovered to be questionable,” Parry quoted him as saying. “The story would lead some investigators to spend time and effort running into blind alleys, with the result that eventually the whole story would be discredited.”

 Teacher, sailor, soldier, spy – Oswald’s convoluted professional curriculum was worthy of a John Le Carré novel.

 A prize-winning poet and literature professor who edited an acclaimed book on Shakespeare’s influence in Europe, he claims to have befriended the German novelists Hermann Hesse and Thomas Mann, as well as the poets Giuseppe Ungaretti and William Carlos Williams.

 Born in Vienna to Jewish parents in 1931, he taught at Columbia University, fought in the Korean War, served a spell in the merchant navy and joined the CIA in 1966, according to his own account.

 His first job with the Agency, he told me, was helping the Bolivian army hunt for Che Guevara. He participated in the Phoenix Programme in Vietnam and then ran an Agency operation to undermine the business of Freddie Laker, the low cost air travel pioneer.

 The scheme involved the International Health and Recreation Organisation (IHARO), with offices on UN Plaza in New York, which promoted cheap flights to Europe on American university campuses. It was done as a favour to MI6, he claimed, as the British government was worried at the damaging effect of Laker’s enterprise on Britain’s long haul national airline BOAC.

 Airline industry experts I spoke to were sceptical, saying Laker went bust because of his own mistakes. Laker, though, said he thought the plot was plausible. “I wouldn’t exclude anything. It’s very much on the cards,” he told me in a phone conversation. Laker eventually won $8 million in compensation from rival airlines for unfair competition.

 During this time LeWinter was arrested in London, for demanding money with menaces. A Singapore Chinese man who handled the London end of the business had pocketed part of the profits and Oswald had crossed the Atlantic to demand its return.

 Subsequent CIA roles, he claimed, involved acting as James Jesus Angleton’s representative in Israel for a year, and liaison with the Vatican in the last year of Paul VI’s papacy.

 In 1985 LeWinter was imprisoned for importing five tonnes of an amphetamine precursor into the United States. The operation was ostensibly conducted on behalf of the CIA, with Oswald posing as a “Mr Wamma”, and then spending just two years in prison out of a six-year term.

 The judge who convicted him was Donald Trump’s sister, Marianne Trump Barry, and Saul Bellow wrote her a letter of recommendation on his behalf. “He is personally charming and good-natured, nothing of the criminal psychopath about him. He simply suffers from a serious misunderstanding of what is appropriate in the career of a literary man,” the novelist wrote.

 In our conversation in Lisbon Oswald elaborated on the allegations made in his BBC interview, saying he had been present at a meeting in Rome when Henry Kissinger had effectively commissioned the physical elimination of Aldo Moro from General Santovito, the head of the military intelligence service and a member of the anticommunist P2 masonic lodge.

 Moro was kidnapped by the Red Brigades in 1978 and killed after being held hostage for 55 days.

 In an interview with the leftwing Italian magazine Avvenimenti in 1990, he had not been so forthcoming. Asked what he knew about the great Italian mysteries, Moro, Bologna and Ustica, he replied: “On the first two I have only secondhand information and I prefer not to talk about them.”

 Oswald’s accounts of the Al Fayed affair were equally ambiguous.

 The “CIA documents” he and four associates had attempted to sell to Mohamed Al Fayed for $20 million were supposed to demonstrate that the head of MI6 had sought the Agency’s help in organising the car crash that killed Dodi and Diana in Paris in 1997.

 Following his release from prison LeWinter was flown to London and swore a new statement for Al Fayed’s lawyers reaffirming the validity of his original claims.

 In a telephone interview, he told me he knew who was involved but had failed to reach a deal with Al Fayed, even at this late stage, because he wasn’t prepared to accuse former Mossad operatives of being behind the killing. But when we met in Lisbon he had a radically different version of events.

 The whole Vienna operation, he said, had been a disinformation sting from the start, authorised by the number two man at the CIA, Jim Pavitt.

 “I was told that Al Fayed had offered a great deal of money and that the British were very alarmed that with that kind of money floating around somebody would decide to, you know, go into business,” he told me.

 Pavitt told members of the group they should sell the fake documents to the Harrods owner, allegedly adding: “Once he’s paid the money we’re going to say: aha, these documents are false, you dumb shit. And that will so embarrass him and show that there’s nothing behind the whole Al Fayed thing, except some crazy grief or whatever. And he’ll stop and that will be the end of it.”

 Organisers of the plot convinced him to participate by telling him that Al Fayed was dedicated to the destruction of the state of Israel. Those behind the operation “knew that was the way to get to me, because I’m a passionate supporter of Israel.”

 John Macnamara, a former Scotland Yard detective and then head of security for the Harrods organisation, was the man who orchestrated LeWinter’s arrest in Austria, but he came away from the whole confusing episode convinced there was a kernel of truth in the con-man’s tale.

 Macnamara told me he believed LeWinter and two of his accomplices, Pat McMillan and the Czech double agent Karl Koecher, had all genuinely worked for the CIA in the past. “We’re moving into real spook business here. It wasn’t just a con-man,” he said.

 His belief was strengthened by the refusal of US justice authorities to prosecute any of LeWinter’s accomplices and by the contradictory behaviour of the female CIA agent who accompanied him to Vienna on the mission to arrest LeWinter.

 The woman telephoned Langley as soon as the man identifying himself as George Mearah was arrested by Austrian police. “Five minutes later a phone call comes back and, I tell you what, the shutters just went down,” Macnamara told me. “She wouldn’t talk to me. She wouldn’t talk to the FBI. She was a different person. They had identified Mearah as being LeWinter.”

 It is difficult to understand whether there really was an intelligent design behind Oswald’s inventions or whether they grew spontaneously from some psychological flaw; whether he was a delusional Walter Mitty character or the Zelig of America’s secret history.

 As we chatted in his modest apartment in Lisbon he informed me, plausibly, that he was “one of the most intelligent people that you will ever meet”. But he also admitted he had nothing to show for his considerable talents, was lonely, impoverished and fighting the temptation to commit suicide.

 Some of his deceptions seem to have stemmed from a mischievous sense of fun. He told me he had adopted the alias Ibrahim Razin, which he used for the interview with Avvenimenti, in honour of Stenka Razin, “a Russian mythological figure who offers a judge a choice of stories.”

 The explanation he offered to another colleague was more prosaic: he had dreamed it up for a telephone caller after eating a bowl of raisin bran!

 The secret history of the world tends to be written, unfortunately, by characters like Oswald. The serious secret-keepers don’t speak, and the Oswalds sow confusion. His incursions into the troubled history of Cold War Italy have not been particularly illuminating and his stories stack up next to the concoctions of the country’s many homegrown fantasists.

 LeWinter is reported to have died in South Carolina in February 2013. The last time I had news of him was several years ago when a German removals company contacted me by email asking if I knew of his whereabouts.

 The man of many aliases, one of which was Mr Alias, had evidently forgotten a bill.