They were frightened for a long time, then suddenly they were angry. For millions of Americans, anxiety about a jobless, debt-laden future turned to disbelief when it emerged that AIG, the company at the centre of the world’s financial crisis, was handing out £300m in bonuses. It was the superpower’s Sir Fred moment. Just as Britain reacted with fury to the disclosure that Sir Fred Goodwin’s pension pot had been doubled as his bank neared collapse, so the US was shocked. The death threats came soon after. “I want them dead!” said one of a stream of messages that caused AIG staff to travel in pairs, park in well-lit areas, and dial 911 if followed. “I want their spouses dead! I want their children dead! I want their children’s children dead! I want the earth upon which they have walked salted so nothing will ever grow again!”

This was one of the greatest bailouts in history, after the biggest corporate loss in history, during the most serious challenge to world stability since the 1962 Cuban missile crisis. And here was AIG, the recipient of so much taxpayers’ money that the cheques exceed the value of the gold reserves in Fort Knox, paying bonuses to the very people who engineered the catastrophe.

Protesters toured the posh houses on Long Island Sound, an estuary northeast of New York City, with letters for AIG executives describing the plight of homeowners. But they were in the wrong place. Because the man who knows most about AIG’s troubles lives in a stucco-fronted house 3,000 miles away. Some call him Patient Zero: the virus that infected the world financial system was transmitted from a genteel square near Harrods. If you wait patiently in Knights-bridge you will see him, and he appears not to be a risk-taking type. He puts on his red crash helmet and cycles greenly off across the city, politely declining to comment on global calamities. This does not look like a person waiting at the curtains for the arrival of the FBI.

Can one man in London really be to blame for the collapse of capitalism?

Until now, the economic crisis has been seen as a giant intellectual error, and AIG’s multimillionaire employees in England were simply the people who made the biggest mistakes. The first to own up to misjudgment was Gordon Brown’s friend Alan Greenspan — once so revered in his role as America’s central banker that to be photographed with him was as flattering as being seen now with President Obama. “I have found a flaw,” said Greenspan, referring to his free-market philosophy, after the banks started falling over. “I don’t know how significant or permanent it is. But I have been very distressed by that fact.”

Others have repeated this innocent-sounding explanation for the wrecking of so many lives. “There is no fail-safe way to offset this human tendency to collective error,” says Lord Turner, chairman of the Financial Services Authority (FSA). And it is true, of course. Now and again, historical forces come together in a way that is mutually reinforcing, and individual changes that are powerful in themselves become so strong that their effects are wrongly seen as permanent. If 150m people — 2Å times the British population — stop tilling the land and start making things, as happened in China between 1999 and 2005; if the Chinese recycle their export earnings into cheap credit; if interest rates stay low for reasons that seem important at the time (the millennium bug, the tech-stocks crash, 9/11); if new ideas allow you to spread financial risk… well, by now you know the explanations. It became easy to imagine that the world was growing rich because we understood the universe better than our ancestors, until we didn’t.

There is, however, an alternative reading. This says that the furore over bonuses is a convenient distraction from the real causes of the crisis, which go to the heart of how the world is run. There is dishonesty in this collapse, on a scale that is almost too vast to comprehend. There are conflicts of interest in American finance and politics that make our own, dear House of Lords look like beginners. There are frauds so large, and so long-standing, that it can be hard to see them for what they are. And all these things were allowed to thrive in an intellectual atmosphere that tolerated no dissent. This reading is optimistic for those who believe in free markets, even if it is pessimistic for the US. “Capitalism has not failed,” says Bernard-Henri Lévy, the French philo-sopher. “We have failed capitalism.” The thesis can be tested through Patient Zero.

The official version is that Joseph Cassano, who occupies the stucco-fronted house near Harrods, brought down a safe and stable company — and by extension, the world — with incompetent gambles. “You’ve got a company, AIG, which used to be just a regular old insurance company,” Obama explained during a recent TV appearance. “Then they decided — some smart person decided — let’s put a hedge fund on top of the insurance comp-any, and let’s sell these derivative products to banks all around the world.” Ben Bernanke, the chairman of the Federal Reserve, adds: “This was a hedge fund, basically, that was attached to a large and stable insurance company.”

Cassano, who ran AIG’s financial-products division in London, “almost single-handedly is responsible for bringing AIG down and by reference the economy of this country”, says Jackie Speier, a US representative. “They basically took people’s hard-earned money, gambled it and lost everything. And he must be held accountable for the dereliction of his duty, and for the havoc he’s wrought on America. I don’t think the American people will be content, nor will I, until we hear the click of the handcuffs on his wrists.”

This account is as satisfying as it is easy to understand. It treats the blowing up of the world financial system like a global version of Barings, the bank that collapsed in 1995, with Cassano in the role of Nick Leeson. Operating from the fifth floor of a polished white stone building in Mayfair, Cassano’s unit sold billions of pounds of derivatives called credit-default swaps (CDS), allowing banks to buy risky debt without attracting the attention of regulators. AIG took the fees, but did not have the money to pay up if the loans went bad. By the time the music stopped, European banks had protected more than $300 billion of debt with this bogus “insurance”. And that is just one corner of a web of risk extending to over 1,500 big corporations, banks and hedge funds. In a 21-page paper known as the Mutually Assured Destruction memo, AIG claims that if the bailouts stop and the company is allowed to go bust, it will take the world with it. Cassano must have played with handcuffs as a child: he is the son of a Brooklyn cop. Now he waits for the fallout.

But the official version overlooks many things, including episodes of fraud at AIG that go back at least 15 years. It fails to explain why Public Enemy No 1 was allowed to leave the company on generous terms, with a retainer of $1m a month and up to $34m (£23m) in bonuses. And it does nothing to tell us why other big companies, whose profits looked as smooth and certain as AIG’s in the good times, are also fighting for survival.

When Forbes published its first list of the world’s biggest companies in 2004, AIG ranked third, after Citigroup, the dying bank, and General Electric, the industrial giant now drowning in its own debt. If you can think of a risk to insure, AIG was there: the company even made plans to survive a nuclear holocaust. It was built into a behemoth by one of the 20th century’s corporate titans, Hank Greenberg. Less famous than the other insurance legend, Warren Buffett, Greenberg gave shareholders a return of 14% a year, and was equally loved. “I just think you are the most stupendous, unbelievable person in the entire industry, the entire world,” one investor told an annual meeting, without irony.

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