Russia’s FSB spy service asked Carsten Linke last autumn via a courier to pass on precise information on the positioning of the Himars and Iris-T rocket systems that had been supplied to Ukraine by the US and Germany, Der Spiegel reported on Friday.

German prosecutors are said to believe that it is unlikely that Mr Linke was able to pass on the information.

In return, the FSB likely paid the suspected German spy in cash. Investigators have found an envelope with a six figure sum in euros in a locker that belonged to him, the magazine reports.

But the question being asked in Germany now is how many more double agents are there.

As a Russian mole, he would have had access to critical information gathered since Moscow invaded Ukraine last year. He may have obtained high-level surveillance, not only from German spies, but also from Western partners, like the C.I.A

Privately, three officials familiar with the investigation — who requested anonymity in order to share details because discussing the inquiry publicly is illegal — worry the case could be the tip of an ominous iceberg.

“Recruiting other spies is the top tier of espionage,” one of the officials said. “And our technical reconnaissance unit is one of the most important departments of the B.N.D. To find someone relatively high up there? That makes this case explosive.”

The case has already led to a second arrest — that of a Russia-born accomplice, who acted as a courier, and, according to one official, brought some 400,000 euros in cash to Mr. Linke from Moscow for his information.

That's a lot of money, but early indications don't show Linke living beyond his means or having any debt. He didn't need the money in other words. Instead, Der Spiegel and the NY Times are suggesting his motive may have been political.

At work, Mr. Linke had openly told colleagues he felt the country was deteriorating, and he was particularly disdainful of its new center-left government, one of those following the inquiry said

One German politician following the investigation worries that some military and intelligence officials still admire Russia and aspire to closer relations, even after the invasion of Ukraine.

“It’s a kind of conviction, wanting to cooperate with Russia — it’s a romantic belief,” the official said. “I worry there are many others who hold that conviction in our security services.”