Spanish police have arrested a whistleblower who leaked thousands of documents exposing an alleged tax evading scheme at HSBC.
Officials detained Herve Falciani, a former computer analyst at the Swiss branch, in Madrid tonight while he was on his way to a conference, a police source said.
'He was arrested in Madrid, in the street,' a top official told AFP, adding the arrest was made at the request of Switzerland, which is seeking his extradition.
A Swiss court in 2015 convicted Falciani, a French-Italian national, of aggravated industrial espionage and handed him a five-year prison sentence.
Falciani was due to take part in a debate at the Comillas Pontifical University titled: 'When telling the truth is heroic: flushing out tax dens.' with journalists from Spain and France.
Police sources said the international arrest warrant issued by Switzerland reached them on March 19.
Falciani, credited with the biggest leak in banking history, was arrested in Barcelona in July 2012.
A Spanish court refused to extradite him in May 2013, saying he had revealed information about potential crimes.
The names on the so-called Falciani list helped Spanish tax chiefs unearth the names of 659 Spanish tax fraudsters.
Internet freedom platform Xnet, co-founded by Barcelona-based theatre director and activist Simona Levi, hinted today's/yesterday's (WED) arrest was an attempt at a trade for Marta Rovira and Anna Gabriel, the pro-independence Catalan politicians now in Switzerland who are being prosecuted by a Spanish judge.
It tweeted: 'Arrest of Herve Falciani. Corruption whistleblowers being used for a bargaining tool. What sort of justice is that?'
The Swiss government has already said it doesn't extradite for 'political crimes.'
He did not attend his trial and has avoided Switzerland ever since.
Falciani leaked a cache of documents allegedly indicating that HSBC's Swiss private banking arm helped more than 120,000 clients to hide €180.6 billion ($222 billion) from tax authorities, sparking the so-called 'Swissleaks' scandal.
The so-called 'Snowden of tax evasion' and 'the man who terrifies the rich' then obtained access to a massive database of encrypted customer information.
He took the client list in 2007 and went to Lebanon with his mistress the next year planning to sell the data. Swiss authorities described it as 'cashing in'.
Yet suspicious bankers in Lebanon were not interested in buying the dubiously sourced client list and at least one tipped off their Swiss counterparts to Falciani's activities.
Falciani then got in contact with European fiscal authorities and began passing them the pilfered information, which prompted numerous tax evasion audits.
Falciani rejects that he was only seeking financial gain, insisting he had wanted to expose how banks support tax evasion and money laundering.
He travelled to Spain by boat in July 2012 and was arrested in Barcelona on an international warrant seeking his extradition to Switzerland.
Falciani then spent a couple of months in a Spanish prison.
In 2013, Spain's High Court ruled against extraditing Falciani on the grounds that the charges he faced in Switzerland are not considered crimes under Spanish law.