The Swiss federal prosecutor, Carla Del Ponte, said Switzerland was holding one Israeli agent and had issued warrants for four others on charges of breaking into an apartment building in Berne and planting bugging devices.
For unexplained reasons, the four fugitives, who are assumed to have left the country, were released after being held briefly by police. The police had been called to the scene at 2am by a woman who could not sleep and saw strangers behaving suspiciously. "We have enough elements to prove Mossad is involved," Ms Del Ponte said. She added that the target of the eavesdropping operation was a foreigner but not a diplomat.
Both governments are eager to clean up the mess as painlessly as possible, but the story was leaked to the Israeli mass-circulation Tel-Aviv daily, Yediot Aharonot. Uzi Landau, chairman of the parliamentary foreign affairs and defence committee, called for those officials who knew of the Swiss fiasco to be given lie-detector tests. "The naming of people, places, methods of work, causes tremendous damage to the national security of Israel," he said.
Intelligence agencies routinely spy in each others' countries, whether or not they are friendly. But the timing could not have been worse for Mossad. The once-vaunted external security service was already in disarray after a commission, investigating a botched attempt to assassinate a Hamas official in Jordan last September, condemned the Mossad chief, Danny Yatom, for faulty planning.
The Swiss disaster precipitated General Yatom's resignation on Tuesday, amid reports of a mutiny in the upper reaches of Mossad over his refusal to go. That is probably why the story was leaked, it is suspected, by a disaffected Mossad officer.
Benjamin Netanyahu, the Prime Minister, is expected to name a replacement within a week. General Amiram Levine, chief of the army's northern command, is emerging as a front-runner. He was Mr Netanyahu's commander in the Sayeret Matkal, Israel's SAS.
The most likely outcome is that the arrested man will be tried, fined and speedily packed off home. That is what happened in 1991, when four Israelis were caught in similar circumstances bugging the Iranian embassy in Cyprus.