Four bankers with Zurich-based Credit Suisse Group were indicted Wednesday on conspiracy charges, accused of helping U.S. taxpayers hide as much as $3 billion in assets from the IRS.

Arrest warrants have been issued for all four, who are believed to be in Switzerland: Marco Parenti Adami, Emanuel Agustoni, Michele Bergantino and Roger Schaerer. All are Swiss citizens except for Adami, who is Italian.

Prosecutors allege in the indictment that the conspiracy goes back as far as 1953. The indictment alleges that as of late 2008 Credit Suisse was maintaining thousands of secret accounts for U.S. customers with as much as $3 billion in assets.