The trial in a Frankfurt court of a Swiss private investigator accused of spying on the tax authorities in the German state of North Rhine-Westphalia got underway on Wednesday.
The 54-year-old allegedly acted on behalf of the Swiss intelligence service trying to uncover a series of thefts of CDs with data on suspected tax dodgers who held money in Swiss banks, according to German prosecutors.
The former police officer is also believed to have planted a mole in the tax authorities – an accusation the suspect has denied.
However, proceedings were suspended shortly after the opening of the trial on Wednesday for the two sides to agree a plea bargain.
The presiding judge said the defendant might be let off with a suspended prison sentence if he reveals credible details of his spying activities, notably the payment of at least €60,000 (CHF69,000) by the Swiss intelligence service.
The trial is due to resume in the middle of next week, according to officials.
Relations between the two countries have been strained ever since the spy was discovered and arrested in Germany last April. He allegedly worked for the Federal Intelligence Service between 2011 and 2015.
For its part, the Swiss Office of the Attorney General has been investigating several German tax investigators for alleged industrial espionage in Switzerland over the past few years.
Over the past decade, the government of North Rhine-Westphalia has bought at least 11 CDs with data about Germans with bank accounts in Switzerland. They have paid millions of euros to try to recover money hidden by suspected German tax dodgers.
The tax evasion spat has been running since the financial crises of 2008 and the subsequent listing of Switzerland as a harmful tax haven by the OECD.
swissinfo.ch with agencies/urs