One former director general of the Defense Ministry, Evangelos Vasilakos, calculated that Greece spent as much as $68 billion on weaponry over the next 10 years, much of it borrowed money. To win these deals, which involved the approval of military and Defense Ministry officials, as well as Parliament, arms dealers probably spent more than $2.7 billion on bribes, according to Tasos Telloglou, an investigative reporter for the Greek daily newspaper Kathimerini, who has written extensively on the subject.

Mr. Kantas, he said, could not make deals, but had the power to disrupt deals because he was considered knowledgeable about weaponry. “He was basically a toll station,” Mr. Telloglou said.

Mr. Fraggos and other experts worry that the prosecution team behind Mr. Kantas’s arrests is being starved of the resources it needs to deal with an ever-widening pool of information. The four prosecutors work in a windowless converted storage room with their desks jammed together. The unit’s chief, Eleni Raikou, appointed last August, paid for the installation of new wall outlets and light switches herself.

But the team appears undeterred. In the wake of Mr. Kantas’s first testimony in December, they have made several more arrests, including the representatives of several German arms manufacturers and a subcontractor in the German submarine deal, who recently provided prosecutors with details of the bank accounts he used to transfer about $95 million worth of “useful” payments.

In an odd twist, Mr. Kantas, 72, was apparently tripped up by his own banker, according to his lawyer, Yannis Mantzouranis. Like many other Greeks, Mr. Mantzouranis said, Mr. Kantas would bring bundles of cash to his banker, who would fly to Switzerland to make the deposits when enough cash had accumulated to make the trip worthwhile.

At one point, however, Mr. Kantas’s banker lent €500,000, about $680,000, of Mr. Kantas’s cash to representatives of the German telecommunications giant Siemens. Then, the banker allowed Siemens, which is under investigation for bribing officials over various contracts in Greece, to wire a deposit directly into Mr. Kantas’s Swiss account with Dresdner Bank.

Investigators looking into Siemens found Mr. Kantas’s name on a list of people the company had sent money to, his lawyer said. Mr. Kantas was forced to explain where the €500,000 in his account came from. At first, he told investigators it was from the sale of some paintings. But they raided the home of the supposed buyer and found evidence that the paintings had been in his possession since the 1980s.