A director at Germany’s spy service was picked up on suspicion of passing intelligence to Russia. German officials and allies worry just how deep the problem goes.

The small Bavarian town of Weilheim, where a director of Germany’s spy agency lived and was arrested in December on suspicion of spying for Russia.Credit...Ingmar Nolting for The New York Times

Erika Solomon, based in Berlin, traveled to Weilheim in Oberbayern, Germany, to write this article. Christopher F. Schuetze reported from Berlin.

Feb. 17, 2023, 10:11 a.m. ET

A few days before Christmas, a convoy of security vehicles invaded a quiet corner of Weilheim, a quaint Bavarian town of pastel squares and fastidiously kept cobblestone streets. Their target seemed as unassuming as the setting: a local children’s soccer coach.

Before then, nothing had stood out about the man, fellow coaches recalled. He was not short, but not tall — friendly, yet never wanting to discuss anything but soccer. Grasping for words, most landed on the same choice: “unremarkable.”

That changed when they learned he had been arrested on charges of treason and spying for Russia in one of the gravest espionage scandals in recent German history.

The coach, a 52-year-old former German soldier, worked for Germany’s Federal Intelligence Service, or B.N.D., as a director of technical reconnaissance — the unit responsible for cybersecurity and surveilling electronic communications. It contributes about half of the spy agency’s daily intelligence volume.