“I never imagined there would be such a reaction, that it would be on every television channel and that we would receive media requests from all around the world,” one of the reporters, Bastian Obermayer, 38, told AFP.
Germany's second-biggest daily in sales, the Sueddeutsche received from an anonymous source more than 11 million documents of the Panamanian law firm Mossack Fonseca that cast a harsh spotlight on the shady financial dealings of many of the world's rich and powerful.
The liberal daily shared the massive leak with a consortium of hundreds of international investigative journalists who have mined the mountains of data for more than a year.
Since Sunday, the revelations have brought down Iceland's prime minister Sigmundur David Gunnlaugsson, forced the resignation of a senior UEFA official and raised the heat on British Prime Minister David Cameron and Argentine President Mauricio Macri.
“We are still in the middle of the revelations,” said the other journalist, who has a confusingly similar surname, Frederik Obermaier, 32, speaking at the newspaper's headquarters in Munich.
“In the coming days, there will be more topics that will make big headlines in many countries.”
'Destroy the system'
In the mass leak, “we are seeing the most different types crimes, we see how the drug cartels launder money, that arms merchants are implicated, that sanctions are being circumvented, we are seeing tax fraud,” said Obermayer.
“If politicians really want to stop it, they must act now.”
“We really need a hammer to destroy the system of offshore companies,” he added, arguing that “the policy of small steps is not enough”.
The data showed that, as national governments take steps against tax cheats, “they adapt, they find new ideas” to divert and hide their money, he said.
His colleague, Frederik Obermaier, was more reserved: “I think there is a lot of talk, but what will be done in the end is a different thing.”
The reporters said they don't know the name of the source at the origin of the scoop, and that they received the data on offshore companies “more than one year ago”.
“I do not know if it's a man or a woman, or a group. I don't know the identity of this person,” said Obermaier, adding however that “we have become a bit more familiar over the year” with the leaker.
At pains to protect their source, the journalists also declined to reveal whether the person had been in contact again or had reacted to the international reverberations.
But they were clear on the source's “moral” motivation, that the person “wants these crimes to be made public”.
“Our source has obviously seen a lot of this data and thought it had to be published,” said Obermaier, while his colleague stressed that the source “wants Mossack Fonseca to cease operations”.
As well as the published news reports, the two journalists plan to release a book in Germany – titled “Panama Papers: the story of a global revelation” – that will explain the whole story of the leak.
'Future of journalism'
It was Bastian Obermayer who received the first contact from the anonymous source, offering the explosive information.
On the choice of Sueddeutsche, “we can only speculate on the reasons why we were contacted”, he said.
Founded in Munich after the Second World War, the broadsheet is considered one of Germany's major newspapers of record, along with the conservative Frankfurter Allgemeine Zeitung, and is number two in sales after tabloid-style Bild.
Having initially reacted in a “sceptical” way, Obermayer said he soon realised, together with his colleague, that the initial documents received were genuine.
Later they decided to share the treasure trove of data in a massive research project with journalists from around the world.
The future of journalism lies in international cooperation,” Obermayer said.
“We are always stronger together.”