TEMPO.CO, Jakarta - Last year was Marina Walker Guevara's busiest time. She had to face piles of documents, layers of digital data, and, most importantly, she was commanding hundreds of journalists from 80 countries who collaborated on investigating and publishing the Panama Papers.

The report involves 2.6 terabytes of data on companies set up in tax-haven countries like Panama or regions like the British Virgin Islands. The companies' owners are a mix of politicians, public officials, thieves, drug lords, billionaires and celebrities, including world-class athletes and sports people.

Containing information dating back from 1977 to early 2015, the report provides an intriguing picture of offshore companies whose intentions are clearly to evade paying taxes. Not surprisingly, this has become the accepted method of criminals and corruptors in attaining benefits from the practice of tax evasion.

Guevara admits that the lengthy investigation, which began from a leaked financial document out of the legal firm Mossack Fonseca, was arguably her most difficult assignment in her journalistic career. "Compiling such a huge data is not an easy job," said Guevara, responding in an interview by Skype, last week.

But she never gave up. To the Argentina-born journalist, investigative journalism is a world she has dealt with since her youth in her home country, where corruption scandals had become very detrimental. "Together with the International Consortium of Investigative Journalists (ICIJ), I had the chance to be involved in a global-scale investigative project," said Guevara, a mother of two children.

Indeed, it was not the first time that she and her associates at ICIJ collaborated on such a project. She was involved in such publications as the Swiss Leaks, the Lux Leaks and the Offshore Leaks.

Speaking to Tempo reporters Philipus Parera and Raymundus Rikang, Guevara shared her views on the challenges she faced while working on the Panama Papers, from trying to get the data to the offers from governments for a data exchange. Excerpts:

How did the investigation on what later became the Panama Papers begin?

Over a year ago, an anonymous source contacted the Suddeutsche Zeitung (SZ) and submitted encrypted internal documents from Mossack Fonseca.

The Suddeutsche Zeitung decided to analyze the data in cooperation with the International Consortium of Investigative Journalists (ICIJ). ICIJ had already coordinated the research for past projects that SZ was also involved in, among them the Offshore Leaks, the Lux Leaks and the Swiss Leaks.

Who first contacted the German newspaper Suddeutsche Zeitung and leaked such a huge pile of documents?

No. I can't tell you that because we don't talk about sources. But it's someone who got the one and only documents and someone who wants to expose crimes.

How did ICIJ choose which media and which journalists from around the world to work with in this project?

We work with journalists that we know, we trust, and we have worked with before. We also look at the media organizations to make sure that they are going to be supportive of the investigation. We make sure that the journalists can collaborate and be able to work in a team.

Did you have to involve hundreds of journalists?

You know that corruption is local (in nature). So we needed eyes from all the corners of the world to give information and find great stories. We needed to build the story from the local perspective and then we build the global picture.

A number of countries have asked their journalists involved in the investigation to submit the list of local figures listed in the Panama Papers. Is that acceptable?

Governments have asked us to give the data and not to show (publicize) the data. The reporters have to refuse because we know that journalists must work independently. We should not collaborate with governments. We have had many such cases in Finland, the UK, and the US. In many of those countries, the governments have approached their journalists to get the data.

In Indonesia, the government also asked Tempo to share data on some tax payers listed in the Panama Papers. But we have refused.

I certainly hope that Tempo will refuse any attempts by the government to exchange data.

Did the US government also ask a copy of the Panama Papers?

Yes. In New York, the prosecutor asked to have the data and we welcome the government's intention to investigate this matter for the public interest. But they did not collaborate in the investigation.

After the publication of the Panama Papers, Iceland's Prime Minister Sigmundur David Gunnlaugsson and the Spanish minister of energy, industry and tourism, Jos Manuel Soria, resigned. Meanwhile British Prime Minister David Cameron is facing calls to disclose his tax returns. Did you expect this to happen when you began this investigation?

That is one of the important revelations of the Panama Papers. How many world politicians, leaders are found to be in such tax havens. This is important because world leaders are responsible for fixing the financial system, and how the powerful and the rich play by different rules. (*)

Read the full interview in this week's edition of Tempo English Magazine.