German clients of Swiss bank UBS evaded around 204 million euros ($267 million) in taxes, the prosecutors' office in Bochum said on Tuesday.
The undeclared funds were revealed after a data CD bought for 3.5 million euros by authorities in North-Rhine Westphalia was evaluated, uncovering data on investments worth more than 3.5 billion Swiss francs (2.3 billion pounds).
It was unclear how much of this was not declared to the German tax man, the Bochum prosecutor said, adding that an initial estimate showed clients had stashed assets and profits equivalent to 204 million euros in unpaid taxes at UBS.
"As part of the investigation we are looking at whether bank employees helped clients evade taxes," the prosecutor said.
A UBS spokesman said the bank did not support efforts by clients to evade taxes.
The revelations come as the German government is making a last-ditch bid to salvage a deal with Switzerland to tax assets stashed by German citizens in Swiss bank accounts.
Germany has convened a mediation committee between the upper and lower houses of parliament to help salvage the tax agreement.
Rather than wait for a political compromise in Berlin, NRW finance minister and SPD party member Norbert Walter-Borjans have continued to make use of stolen client data.
Further evaluation of the CD could yield additional undeclared funds, Walter-Borjans said, adding he would not ratify an agreement in Berlin which, in his opinion, was too lenient.
Prosecutors accompanied by around 80 tax inspectors searched apartments and offices as part of a probe to unearth undeclared tax assets bunkered in Swiss bank accounts, the Bochum prosecutor said.
The data CD revealed information about 750 foundations set up by clients. Of these, around 115 are being probed.
In 135 cases, tax evaders had already turned themselves in to authorities before a formal investigation had begun the prosecutor's office said. ($1 = 0.7650 euro = 0.9261 Swiss franc)
(Reporting By Matthias Inverardi and Oliver Hirt; writing by Edward Taylor)