A 54-year-old man, identified only as Daniel M, was arrested on Friday. His lawyer told a Swiss newspaper he was suspected of trying to find out how German states have obtained CDs containing details of secret Swiss bank accounts set up by Germans to evade tax.
According to German media reports, the spy, a former policeman, worked for the Swiss Federal Intelligence Service (FIS), enlisting moles inside the finance ministry of Germany’s most populous state, North Rhine-Westphalia (NRW), to uncover the identities of German tax investigators.
The Swiss man is suspected of having spied in North Rhine-Westphalia since early 2012.
German investigators suspect the intelligence he gathered would then be used to accuse specific German officials of violating Swiss banking laws and engaging in commercial espionage.
Switzerland has publicly spoken out against the practice of buying data stolen from Swiss banks.
However, since 2010 NRW has paid whistleblowers almost €18m (£15.2m, $19.6m) for data CDs revealing secret Swiss bank accounts in a bid to tackle tax evasion by German taxpayers.
As a result, NRW said it has secured nearly €7bn in revenue as the CDs led 120,000 German citizens to self-report Swiss bank accounts.
On Tuesday, the FIS defended domestic efforts to uphold Swiss laws, reported Reuters.
“When someone in Switzerland uses illegal methods in Switzerland to steal state or business secrets, that is espionage, and we have the task to fight that,” FIS director Markus Seiler told reporters at a briefing in Bern.
“The FIS is active at home and abroad,” he said. Asked if this included Germany, he said: “I say simply nothing.”
Meanwhile, NRW finance minister Norbert Walter-Borjans compared the latest revelations to a “spy thriller”.
“The scandal reaches new proportions when spies sign up informers in the finance administration, in order to spy on successful NRW tax investigators and play into the hands of people who make billions in profit at the expense of society,” he told German media.
“It’s hard to believe that such a spy thriller took place not on the screen but on our own doorstep.”
The German federal government has asked Switzerland for an explanation concerning the alleged spying.