Stephen Curtis confided with friends that he feared for his life
British lawyer Stephen Curtis played a crucial role in managing the fortunes of some of the world's richest men - the so-called Russian oligarchs.
Radio 4's Jenny Chryss examines his life, and explores why his untimely death has given rise to conspiracy theories.
When a helicopter crashed near Bournemouth airport in March 2004, it was seen as a tragic accident.
The pilot of the twin-engine Augusta 109 died instantly, along with his only passenger, when it came down in fields about a mile from its destination.
Air accident investigators began their usual task of sifting through the wreckage, the police opened an inquiry and the coroner was informed.
But behind the scenes, the crash was sending shock waves all the way to the Kremlin.
The passenger who died was millionaire lawyer Stephen Curtis.
After work at his plush London offices, he regularly made the short flight to Bournemouth, and then on in his chauffeur driven car to his eighteenth century castle in Portland.
In the weeks after the accident, details of his work for wealthy international clients began to emerge. Of particular interest to investigators were a small group of Russians who, in the 1990s, had begun to seek his services.
They were among the first of a new breed of rich Russian businessmen to emerge from the sell-off of state assets under President Boris Yeltsin.
In return for supporting his election campaign, they'd been given places at the front of the queue when the country's major assets were privatised.
In a highly controversial deal known as "loans for shares", and a series of rigged auctions, they acquired assets worth billions of dollars at a fraction of the real price.
Embracing capitalism with fervour, 22 of these businessmen quickly rose to the top, owning between them 40% of the Russian economy.
The term "Russian oligarch" was born.
Yukos is a shadow of its former self
While millions of ordinary citizens were struggling to survive in the new market economy, the oligarch's priority was transforming the outdated inefficient companies they had inherited into profitable western-style businesses.
It was to western financiers and lawyers like Mr Curtis that they turned for help.
They needed western business skills, not only to help their profits grow, but to protect them from the tax authorities back home in Moscow.
And leading the charge to the doors of their London offices was the man who was to become the most important of all the oligarchs, Mikhail Khodorkovsky.
The former Young Communist League official had set up a bank, Menatep, and acquired the Yukos oil company for just $300m (£160m).
His early guide to the offshore world was a Geneva based company called Valmet, which also had offices in London and the Isle of Man.
"I liked the way he was creating his business, I liked his approach," Valmet's founder Christian Michel recalls. "Other people just wanted to grab an asset. Khodorkovsky and others had a very long term strategy."
According to Mr Michel, the first job was to teach the Russians the mechanics of doing businesses with international clients, setting up contracts and negotiating loans with international banks.
But as the profits grew, so did the need to protect them.
Valmet began working with the ever expanding business empires of Khodorkovsky and others by setting up complex offshore structures in tax havens around the world.
These structures were to prove crucial to saving the oligarchs' fortunes when the rouble collapsed in 1998.
Khodorkovsky became Russia's richest man, worth more than $13bn, and it was Valmet who introduced him to Mr Curtis.
By the late 1990s, Valmet and Mr Curtis had moved into new offices at the top of Park Lane, where between them they were handling large amounts of offshore business on the Russian billionaire's behalf.
But in their rise, oligarchs like Khodorkovsky were beginning to upset people, among them the minority shareholders who claimed they had been deprived of their investment, and the ordinary Russian people struggling to get by.
Riches to rags - Mikhail Khodorkovsky was sent to prison
Khodorkovsky himself was in deeper trouble.
In October 2003, he was arrested by police while his executive jet was refuelling at a Siberian airport.
He was charged with fraud and embezzlement. He was tried and convicted last year in what was criticised by many as a show trial, and is now serving nine years in a Siberian jail.
His arrest thrust the secretive Mr Curtis unwillingly into the limelight.
Journalists talked of a mystery man in Gibraltar who now controlled Yukos, out of reach of the Russians.
He became the only director of Group Menatep, the Gibraltar company which controlled more than 50% of Yukos on behalf of the now jailed or exiled owners.
The secrets Mr Curtis held about the offshore money flows in and out of Yukos explain the conspiracy theories which continue to surround his death.
These were further fuelled by the discovery that, perhaps to protect himself, he had begun to pass information to the British authorities.
"In the inquest into his death it emerged that he'd told a close relative that if he were killed it would not be an accident," says former Financial Times reporter Thomas Catan. "The coroner himself said that the story contained many ingredients of an espionage thriller."
Ultimately, the inquest decided that there was not the evidence to point to foul play, and ruled Mr Curtis' death was an accident.
Yukos is now bankrupt, and Group Menatep in Gibraltar is suing the Russian government for a record £25bn on behalf of Khodorkovsky and his partners.
The Park Lane offices from which Mr Curtis helped control the Yukos empire are empty.
Piles of uncollected mail are the only clues to its former role.
From The Kremlin to Knightsbridge is on Radio 4 at 2000BST on Monday 2 and 9 October, or online at Radio 4's Listen again page.