Eventually, the office of Chancellor Angela Merkel became involved and a complaint was made to the Kremlin about the lack of cooperation. On Wednesday, Ms. Merkel defended the decision to expel the Russian diplomats as a consequence of the inaction. “We took this step because we did not see that Russia was supporting our investigation of this murder,” she told reporters in Watford, England, where Western leaders are gathered to celebrate NATO’s 70th anniversary.

Image The Berlin police distributed an image of the suspect. Credit... Berlin police department

According to the prosecutor, the suspect was carrying a Russian passport when arrested on Aug. 23 that the Russian authorities confirmed as authentic. Although the document identified him as Vadim Andreevich Sokolov , investigators said at the time that they believed the name was fake.

The suspect had arrived in Europe on a flight from Moscow to Paris and entered on a visa previously issued by French authorities that allowed him to work and move freely throughout the European Union, the prosecutor added. Three days later, he continued to Warsaw, where he checked into a hotel for a five-night stay. After only three nights, however, he left and did not return. The following day he was arrested in Berlin.

The man’s visa said he had been employed as an engineer since 2017 at a company called Zao Rust, based in St. Petersburg. But according to records in Russia, the company was in “reorganization” in 2019 and had only one employee in 2018, according to the prosecutor.

When the German authorities tried to contact the company, they discovered that the fax number listed for it was the same as that of two other companies, both belonging to the Russian Defense Ministry, the prosecutor said.

Mr. Khodorkovsky , the founder of the Dossier Center, said in an interview that, “The Kremlin is no longer ashamed of reasonable suspicions that it carries out murders in Western Europe.”