THIS is the story of how a global network spent months digging into the hidden transactions of the rich and famous, with their incredible findings implicating world leaders, celebrities and powerful businessmen.

The Panama Papers are the “biggest leak in journalism’s history”, made up of 11.5 million documents, or 2.6 terabytes of data, from law firm Mossack Fonseca.

They are evidence of tax evasion, secretive deals free from government oversight and links to corruption.

The Panama-based firm sells anonymous offshore companies around the world. Owners can use these “shell” firms to cover up such business dealings.

It’s particularly concerning because the companies using Mossack Fonseca are owned by or linked with some of the richest and most influential people on the planet, many of whom are already accused of involvement in serious crime, including drug traffficking, terrorism, arms dealing and trading with “rogue nations” such as North Korea.

The investigation into the papers was co-ordinated online by the International Consortium of Investigative Journalism, with reporters across the world sifting through the documents.

Only one journalist, Bastian Obermayer from Germany’s Suddeutsche Zeitung newspaper, knows the identity of the leak, who has risked his life exposing these secrets.

Marian Wilkinson, from the ABC’s Four Corners, was at the heart of the ambitious investigation.

Mossack Fonseca’s 200,000 clients include associates of Russian President Vladimir Putin, who quietly shifted $2 billion through banks and shadow companies, and Icelandic Prime Minister Sigmundur David Gunnlaugsson, who held millions in bonds during the country’s financial crisis.

They also include companies controlled by Chinese president Xi Jinping, Ukrainian president Petro Poroshenko, the King of Saudi Arabia, the prime minister of Pakistan, the president of Azerbaijan’s children and even the late father of British prime minister David Cameron.

Celebrities are implicated too — footballer Lionel Messi, businessmen involved in the FIFA corruption scandal and actor Jackie Chan, who had at least six companies managed through the Panama firm.

The papers also show New Zealand is being used as a tax haven by foreign politicians.

It is a discovery with the potential to change the world.

‘WHO THE HELL ARE MOSSACK FONSECA?’

This was Ms Wilkinson’s first reaction after a colleague in Washington brought her into the investigation, she told news.com.au.

Mossack Fonseca has 30 offices around the world, including in Australia, and is one of the most active players in the world of tax havens — offshore centres where the wealthy can place money tax-free and conduct under-the-radar transactions.

“As soon as I began looking, I realised they were one of the more renowned operations in the offshore world,” Ms Wilkinson said.

“There were some pretty bad people in there. We realised the value of the material and the fact it was global, and the fact Mossack Fonseca had the most extraordinary array of people using their services.”

There was, for example, Syrian president Bashar al-Assad’s billionaire cousin Rami Makhlouf. Emails from a senior partner at the firm revealed they were still working with him when “Syrians were burning his effigy in the street.”

It was clear, said Ms Wilkinson, just how far Mossack Fonseca “was prepared to push the boundaries of what was ethical or acceptable”.

VISITING OFFSHORE TAX HAVENS

Many of the 800 Australians using Mossack Fonseca went through an office in the popular — and beautiful — tax haven of the British Virgin Islands.

Ms Wilkinson, along with many journalists working on the project, wanted to go and see what was happening for themselves, but found the Caribbean territory was “extremely sensitive” and even “hostile” about letting them in.

The Australian journalists who wanted to follow up the story couldn’t obtain work permits, a Canadian who visited was turned back at the airport. The Four Corners team, whose investigation airs tonight at 8.30pm on ABC, eventually got in by chartering a boat from the American Virgin Islands and entering as tourists.

But the authorities had Ms Wilkinson’s name on an immigration stop list and they were searched on arrival and monitored throughout their visit.

“The Mossack Fonseca offices there were just one floor of a small building on a side street,” said Ms Wilkinson. “This is what tax haven offices are like, it’s clear no one seriously does any work there.

“There are almost half a million companies going through there. It brings home the artificiality of it all. Even if you get the co-operation of the authorities, you’re not going to get anywhere.”

D-DAY IN PANAMA

When the Australian team met 25 other journalists in the central American country, they learnt even more about the troubling paper trail. It led to arms dealers, drug dealers, former intelligence agents, the former Panamanian president and businessmen involved in the Petrobas corruption scandal surrounding the Brazilian president.

The group descended on Mossack Fonseca’s headquarters to confront the organisation, but were blocked by security guards. After almost an hour of fraught negotiations, the company responded by sending out a representative with a statement listing their total denial of all allegations.

Shortly before today’s revelation, the firm emailed all clients saying it believed there had been a data breach. The Panama government also put out a press release to its embassies and consulates

trying to shore up credibility.

But Ms Wilkinson believes “the horse has bolted. This secrecy breach will affect its standing with clients as discreet”.

Mossack Fonseca’s 800 clients in this country are being investigated by the Australian Taxation Office, and that’s being replicated on four continents.

“They will have a hard time answering questions from all over the world.”

emma.reynolds@news.com.au