Q: When did you realise you had unearthed a story of global significance?

A: When we found the first links to a head of state – and then another. It was an exciting feeling to have a unique insight into the secret affairs of Iceland's prime minister and then Ukraine's president. The more we kept adding names, the more we dared to hope for a global response.

Q: How did you deal with all that data? It must have presented a technological challenge as much as anything.

A; Yes, it was a huge challenge, and we weren't really experts in this field at all. So we had to learn a lot and we made a lot of mistakes. We lost data and had to start again, we forgot passwords, destroyed hard drives by mistake - and we had to convince our bosses several times to buy us a new computer: bigger, faster and better. In the end they cost as much as a decent hatchback.

Q: Were you ever afraid? What was the most nerve-wracking point for you?

A: We weren't really afraid but it is a strange feeling to investigate the finances of super-rich people who are known for their recklessness, or the illicit funds of dictators, arms dealers, drug cartels and other dangerous people. But we took precautions (for example we took our names off the public registers). Most nerve-wracking were the final weeks, when it all culminated: the legal letters arrived, we had to redo our cross-checks, we met key people involved in the investigations and most importantly we had to finish writing our news pieces and the book.

Q: Is there a case that you're particularly proud of cracking?

A: Obviously the Russian case – the case of Vladimir Putin’s best friend, the godfather of his first daughter, the guy who is at the heart of an offshore network through which more than two billion dollars were funnelled. This guy wasn’t widely known, but we were able to uncover at least part of this secretive network of companies – and we keep finding new connections, for example to the Magnitsky case, allegedly the biggest tax fraud in Russian history.

Q: What was the strangest thing you found?

A: Maybe the fact that Jürgen Mossack himself, the German founder of Mossack Fonseca, was already in the eighties involved with some bad people. He helped to set up companies that held properties for one of the most gruesome drug lords the world has seen: Caro Quintero. Mossack also allegedly helped to launder money from the legendary Brink’s-Mat gold robbery back in 1983. It was shocking to find that Mossack and his partners did business with people like Rami Makhlouf, who is sanctioned and said to be a financier of the Syrian regime – and thus a war that has already cost hundreds of thousands of lives.

Q: Did you think the story itself might leak, with so many people involved?

A: We felt sure it would leak, to be honest. And we were sure we would lose stories along the way. But we are very happy it didn't in the end, and that was because everyone in the team understood that the story was better for everyone if we published at the same time.

Q: What's it been like to see the reaction to the stories around the world?

A: It was fascinating to see how it unfolded – and it still is. You don't have Barack Obama and Vladimir Putin commenting on your work all that often, or the European Parliament setting up an inquiry committee. We’ve seen a prime minister step down and mass demonstrations in several countries – that’s certainly never happened before.

Q: What needs to change to prevent the abuse of shell companies in future?

A: We need registers of beneficial owners for offshore companies – especially those in the British Virgin Islands, which is obviously a British duty. We need more transparency in the banking sector and we need politicians not only speaking out against tax havens but acting against them – even when they are within their own country.

The Panama Papers by Bastian Obermayer & Frederik Obermaier

Published 30 June 2016