Swiss prosecutors are investigating a data leak involving thousands of former Credit Suisse Group AG clients who’d reportedly held $100 billion with the bank, in a case that could dent efforts to boost transparency in the secretive country.

The Attorney General’s Office confirmed it’s investigating suspected acts of corporate espionage, breach of trade secrets and violations of banking secrecy laws after the information on 18,000 accounts was leaked to an international consortium of media. The journalists went on to publish a series of exposes last February under the tagline “Suisse Secrets” which reported that the client roster included drug barons and kleptocrats. 

The probe needed sign off from the federal government because the espionage allegations are considered a “political infraction,” the AG’s office said. The bank declined to comment.

Bern’s blessing for the investigation highlights the lengths Switzerland goes to in order to protect banking secrecy, a principle enshrined in Swiss criminal law. The probe is also likely to intensify international criticism of Switzerland’s tendency to prosecute the whistleblower rather than the criminal activity exposed in the leak. 

An anonymous whistleblower gave the information to German newspaper Sueddeutsche Zeitung, which shared the data with a nonprofit journalism group and dozens of other news organizations worldwide. But Tamedia, publishers of the respected Swiss-German daily Tages-Anzeiger which has worked on such collaborative projects in the past, said it couldn’t work on Suisse Secrets because of a risk of falling afoul of the bank secrecy law. 

When the leaks were published a year ago, CS issued a statement saying that approximately 90% of the reviewed accounts were closed or were in the process of being closed. The media reports “appear to be a concerted effort to discredit not only the bank but the Swiss financial marketplace as a whole, which has undergone significant changes over the last several years,” the bank said. –BLOOMBERG