A German newspaper said Thursday, citing law enforcement sources, that KGB officer-turned-businessman Kovtun made a phone call to his former mother-in-law, living in Hamburg, on December 12 from Berlin.
Police confirmed that that the signal came from Berlin, but called it a false trail.
"There actually was a signal from Berlin, and Hamburg police checked this during the night. However, this signal turned out to be a false trail. There is no proof that Mr. Kovtun was in Berlin at this or any other time," a police report said.
Alexander Litvinenko, a Federal Security Service defector and outspoken Kremlin critic with ties to exiled Russian oligarch Boris Berezovsky, died November 23 in a London hospital from a lethal dose of radioactive polonium-210.
Kovtun met with Litvinenko in the British capital shortly before he fell ill, and was himself later diagnosed with radioactive poisoning by doctors in Moscow.
Police in Hamburg launched an investigation into Kovtun after traces of radiation were detected at several sites he visited between October 28 and November 1, including at his ex-wife's apartment. German prosecutors are investigating the businessman, who has a German residence permit, on suspicion of illegally transporting nuclear materials.
In Russia, Kovtun is being treated as a witness in the Litvinenko case.
Another key witness in the case, Andrei Lugovoi, also a former security agent and Kovtun's business partner, was questioned in a Moscow clinic Monday by Scotland Yard detectives and Russian investigators. Lugovoi also met Litvinenko in London around the time he fell ill.