Michael Bachelard – "If I've got $600 million a year... you'll partake in it," Olgario de Castro reassures his mates, his voice caught by a secret recorder as coffee cups clink in the background.

"I want the money, not the power!" he says at one point and, later, of another deal: "Last minute, we'll find $2 million!"

The conversation moves fast. It's often indistinct, full of in-jokes and threads of earlier discussions and it's impossible to say how much is bravado and how much a joke. It could be by any group of business wannabes big-noting themselves in a cafe.

The catch is that, in this conversation, Mr de Castro, the big-noter-in-chief, is a very important man to the fragile state of East Timor. He is the chairman of the board advising the government on where to invest the country's $10.5 billion petroleum fund – "the only money that stands between Timor Leste and even worse poverty and underdevelopment", according to respected local researcher Charles Scheiner.

East Timor goes to the polls this weekend, and the Petroleum Fund is at the very centre of politics there. Last year withdrawals from the fund made up 97 per cent of East Timor's budget spending. Outside of this fund and its earnings, according to the United Nations, the country barely has an economy.

Mr de Castro, a Darwin accountant and part of the tight-knit Timorese expatriate elite, chairs the Investment Advisory Board for the fund. He is also close to the person ultimately in charge of that fund, East Timorese Finance Minister Emilia Pires. The country's Central Bank plays the third key role.

Mr de Castro did not respond to requests for comment, but East Timorese Prime Minister Xanana Gusmao said through lawyers that he was "seeking advice and conducting an investigation" into the recording, after The Age provided it.

The recording, made in December 2010 but given anonymously to The Age by an Australian source last week, shows Mr de Castro being, at the very least, indiscreet and reckless.

Perhaps he is joking about spending millions of dollars intended to protect the future of one of the most impoverished peoples in the world. If he's not joking, his words are considerably more serious.

In response to ribbing from three Australian companions, Mr de Castro talks about opening a $5 million Swiss bank account, and about refusing an offer of a private jet and an apartment in Singapore because "I'd have to explain that".

He says he is going to live in England as part of "a separate deal altogether". Multimillion-dollar sums are tossed around – $600 million a year that he will control and in which his friends can partake, but which the vice-president of the World Bank in Washington had told him "was fraudulent".

There is talk of a $2 million furniture deal which would be approved, Mr de Castro says, but not until January 2011 because "we've got the budget to prepare".

He says he has been offered the job of finance minister in East Timor both by Ms Pires and also by the opposition party, Fretilin. But he exclaims repeatedly that he does not want it because: "I want the money, not the power."

Asked in the midst of this whether he cares about East Timor at all, Mr de Castro says: "Of course! A few billion dollars of infrastructure for free for the country. Isn't that a positive thing?"

And asked if Mr Gusmao is "on your side", Mr de Castro replies: "Xanana is for me. Xanana is for me to make it happen."

This may well be a joke, but for someone in his position, even shooting the breeze on an issue like this is ill-advised. The politics of the petroleum fund heated up considerably last year. Until now the money has been invested conservatively, overwhelmingly in international bonds, but late last year, the Gusmao government changed the rules to allow half to go into equities, and a further 10 per cent as collateral for loans.

The idea was to diversify the country's investments, but the opposition party Fretilin, which set up the fund and its conservative principles, opposed the change, warning it would open it up to the sort of fly-by-nighters who robbed tiny Nauru of all its mineral wealth, mostly through dodgy property deals.

Mr Scheiner, a researcher at the respected East Timor policy analysis group La'o Hamutuk, has also warned against the changes to the fund. Though he says the country's leaders and its people have had long experience of violence inflicted by foreigners, they "may still be a little naive about how easy it could be to steal their resources".

"As a small, inexperienced country with a big bank account, [East Timor] is a tempting target for unscrupulous people who want to convert the nation's petroleum wealth to their personal gain," Mr Scheiner said.

Already one attempt has been made to scam the fund. In September 2009, a proposal was put forward by a group called Asian Champ Investment, that East Timor put $1.2 billion into its private bank account for a year. In return the country would receive $90 million "interest" up front.

"When I told one foreign ambassador about it in 2009," recalls Mr Scheiner, "he said, 'I get emails like that from Nigeria every day'."

But in East Timor, the proposal was given a serious hearing. The minister passed it to the Investment Advisory Board. The board wrote a formal reply, signed by Mr de Castro, recommending the minister reject it.

Curiously, though, the government has been reluctant to release a full explanation of how the proposal got that far. And the Singaporean businessman who proposed the deal to East Timor, Datuk Edward Ong (who claims he only acted as a go-between) had previously been approved by the government for a massive five-star hotel project on the outskirts of Dili – a project which is stalled and well overdue.

The tape, which was recorded in December 2010, 15 months after the deal was scuppered, captures Mr Ong's name, but in confusing circumstances. "He told me that he had the finance approved independently, but... he lied to me," Mr de Castro says, in apparent reference to the Singaporean.

Now that legislation makes East Timor's billions more footloose, Mr Scheiner is worried. "Although Timor-Leste's revenue management system is better than most oil-dependent countries, it is not leakproof and it appears to be weakening," he says. "We are afflicted by the 'resource curse'."