He and Mr. Linke are believed to have first met in 2021, three people familiar with the investigation said, at a yearly festival run by the Weilheim sports club where soccer coaches and their families snacked on coffee and cake or drank beers in the afternoon. The two were put in touch by one of Weilheim’s local AfD members, who once served in the military with Mr. Eller and remains a reservist.
Travel logs and flight records found by a Russian investigative group, the Dossier Center, show Mr. Eller took hundreds of flights to New York; Los Angeles; Dubai, United Arab Emirates; Baku, Azerbaijan; Belgrade, Serbia; Tbilisi, Georgia; Prague; Doha, Qatar; Shanghai; Geneva; and countless Russian cities.
Many trips to his native country were very short, but he usually stayed in the best hotels in Moscow and St. Petersburg, according to the Dossier Center. He also made trips to surprisingly obscure Russian locations, like Nizhnekamsk.
Mr. Eller has been cooperating with the investigators, people familiar with the operation said. Mr. Linke has so far remained silent.
According to people following the inquiry, Mr. Eller has told investigators that he believed that he was working with Mr. Linke on a B.N.D. operation. But German authorities have expressed wariness of his version of events.
Mr. Eller also said he served as a courier, taking documents to Russia and bringing money back. Four times, he said, he passed envelopes of cash late last year to Mr. Linke, one person familiar with the investigation said.
At their last handoff, Mr. Linke’s boldness apparently went as far as to have a B.N.D. agent working at the Munich airport pick up Mr. Eller and collect a final cash exchange for him — an envelope that investigators believe held 100,000 euros.
