Spanish police have arrested a whistleblower convicted in Switzerland for sending thousands of HSBC clients’ secret bank details to tax authorities.
In 2015, a Swiss court sentenced the French national, Hervé Falciani, to five years in jail for industrial espionage. He had fled to France from Geneva in 2009.
He had worked in the IT department at HSBC’s Swiss private banking unit.
Mr Falciani said he wanted to expose massive tax evasion via Swiss accounts.
Last November, HSBC agreed to pay €300m ($368m; £262m) to French authorities to settle a long-running investigation into tax evasion by French clients via Switzerland.
Spanish police sources say they received a Swiss international arrest warrant on 19 March. Swiss authorities say Mr Falciani stole and attempted to sell confidential data, violating Swiss banking secrecy laws.
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Reports say his arrest on Wednesday came just before he was due to speak at a Madrid university about his whistleblowing.
It is a sensitive time in Spanish-Swiss relations, as Spain has issued an international arrest warrant for a Catalan separatist leader, Marta Rovira, who fled to Switzerland in March.
A team at the International Consortium of Investigative Journalists (ICIJ), led by France’s Le Monde daily, published Mr Falciani’s “Swiss Leaks” data, revealing accounts held by more than 100,000 wealthy individuals and legal entities.
The ICIJ said the accounts – belonging to HSBC clients from 203 countries – contained more than $100bn in total.
HSBC says it has tightened up its compliance mechanisms since the violations came to light.
An earlier extradition request from Switzerland prompted Mr Falciani’s arrest in Barcelona in 2012. But in 2013 Spain’s High Court rejected the request, arguing that the accusations were not offences in Spain.