An Austrian man held in connection with the theft of Swiss bank account details and their sale to Germany is believed to have killed himself in prison, news reports said.

Guards at a regional jail in the Swiss capital of Bern discovered the 42-year-old man dead in his cell on 29 September, the Swiss federal prosecutor’s office was quoted saying.

The man had been detained since mid-September on suspicion of economic espionage, reports said.

The man, who wasn’t identified in reports, was held in an investigation into the alleged theft of client data from Swiss banks, which were subsequently sold to German tax investigators, prosecution spokesperson Jeanette Balmer was quoted by Bloomberg as saying.

News of the man's death comes at a time when there have been several cases of stolen private banking data being sold to Western governments. In the noughties, the German government bought data stolen from LGT, the Liechtenstein private bank, for example.

Officials in the German state of Baden-Wuerttemberg said in August they were using information from an informant to identify possible tax dodgers who stashed funds in Switzerland.

“As far as could be determined so far, no third party was involved,” the prosecutor’s statement said. “A suicide seems likely.”

The suspect was an Austrian national, Austria’s foreign ministry spokesman, Harald Stranzl, was quoted as saying.

The man, a native of the Tyrol region of Austria who lived in the Swiss town of Winterthur, sold information on 2,000 account holders of a Swiss bank to the German tax authorities, the Vienna-based Krone newspaper reported, citing unidentified Swiss and German secret service officials.