The men, two Spaniards and a Colombian, have admitted bringing 363g (about 13oz) of plutonium from Moscow to Munich in August as the first instalment of a $267m (£170m) deal. They could hardly deny it, since they were caught red-handed. But they say they are the victims of a government sting. Without the German intelligence services, they suggest, there would have been no crime.
Yesterday the judge said it was not a political trial, but in practice it will be: the German authorities will be on trial almost as much as the men. And there seems little immediate prospect that those who offered the plutonium for sale in Moscow will be caught or brought to trial.
When the smuggling was first exposed, the German authorities did not hide the fact that it had been a form of sting. Their intention was partly to draw attention to what they regarded as the potential dangers in Moscow and elsewhere. It was what Bernd Schmidbauer, responsible for co-ordinating the intelligence services, described as a preventive operation.
A former head of BND, the foreign espionage service, recently said such an operation was perfectly legitimate: "The reason why rats exist isn't that somebody puts out poisoned bait for them."
None the less, a report last month in Der Spiegel on "The BND's bomb swindle" had a dramatic effect in Germany. The magazine published evidence showing the intelligence services had been luring the sellers to market. Der Spiegel gave a precise account of how the sting was set up, with bugged meetings in Madrid and Moscow.
Those on trial in Munich are Justiniano Torres, 38, a Colombian and Julio Oroz, 49, and Javier Bengoechea, 61, both Spaniards. They acted as middlemen and were arrested after the plutonium was seized at Munich airport. Yesterday the judge suggested the court might hand down a more lenient judgment if the BND were shown to have triggered the whole affair.
The suggestion that the intelligence services were actively involved at an early stage caused enormous controversy and prompted the setting up of a parliamentary investigation committee.
The Russians muddied the waters by saying the plutonium did not come originally from Russia but was deliberately sent from Germany to Russia in order to be smuggled out again. Georgi Kaurov, spokesman of the Russian atomic energy ministry, said: "The German public has been deceived ... Bernd Schmidbauer lied the whole time." German experts insist that analysis demonstrates conclusively that the 363g of plutonium came from the former Soviet Union. The only question is which plant it came from.
The Russians have been reluctant to help German investigators, claiming the case has merely been staged in order to give an excuse to "bring the Russian nuclear complex under international control".