The country's office for financial crimes prosecution (FIOD) said dozens of people were suspected of involvement in alleged fraud and money laundering through their use of bank accounts, with assets not disclosed to tax authorities.
Authorities have detained two suspects and seized a gold bar, luxury cars, dozens of paintings, property, jewellery and bank accounts as well as data from thousands of account holders.
AMSTERDAM, March 31 The European Union judicial agency Eurojust said on Friday it had helped coordinate cross-border investigations in a major tax evasion investigation involving millions of euros and spanning several European countries and Australia.
Swiss banks have come under increased scrutiny in recent years amid an global crackdown on tax evasion.
Credit Suisse Group AG's offices in London, Paris and Amsterdam were visited Thursday by local authorities in connection with client tax matters.
Credit Suisse said in a statement that "we are co-operating with the authorities", pointing out that it has applied the Withholding Tax Agreement between the United Kingdom and Switzerland since 2013, along with similar arrangements with France and the Netherlands. Under the OECD's Automatic Exchange of Information, banks pass on information to local tax agencies, which then share it with foreign counterparts.
To be sure, Credit Suisse was hit hard in the past over tax evasion allegations, and was fined $2.6 billion in the U.S.in 2014 and pleaded guilty to helping Americans evade taxes.
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Eurojust said the investigation began in 2016 and it had held three meeting with Dutch, British, French, German and Australian authorities.
"The sheer volume of data and its worldwide scope makes this an exceptional case", said Thierry Boitelle, a lawyer with Bonnard Lawson in Geneva.
To be sure, Switzerland's prosecutor will be of little practical help to Credit Suisse on the ground in France, the Netherlands, the United Kingdom and Australia, where the bank must answer to local, not Swiss jurisdiction.
The Dutch tax authorities said current technology, greater global cooperation and the lifting of bank secrecy are making it easier for authorities to find tax evaders and their money.
Spokeswoman Wietske Vissers said the investigation would "continue for days and weeks" across the various countries. Bank officials declined to comment further.
"Tax dodgers who are the subject of investigation in the various countries all have parked the money in the same Swiss bank", the Netherlands tax prosecutor said.