German police became involved in the international hunt for Litvinenko's killer when Dmitry Kovtun, a Russian businessman living in Germany who had met with Litvinenko on November 1, 2006, the day of his fatal poisoning, was named as a key witness.
German authorities handed the documents to Russia "as an expression of their willingness to cooperate with Russian partners, in response to a request from Russia to provide the Russian delegation with certain materials on the criminal case," said Vladimir Markin, spokesman for the Investigation Committee of the Russian Prosecutor General's Office.
Some of the materials relate to an attempt on Kovtun's life, the spokesman said.
German detectives said at the time they were certain Kovtun had come into contact with radioactive polonium, the substance used to kill Litvinenko, before flying to Britain.
Markin said the case files were handed over during a visit by Russian investigators to Hamburg, which began on July 13. Russia had requested information from Germany on December 27, 2006, but did not receive a reply until this month.
Copies of the German files have already been submitted for translation and will later be thoroughly studied and added to case data being used by Russian investigators, Markin said.
The murder of Litvinenko, an outspoken Kremlin critic who had received British citizenship soon before his poisoning, caused a major diplomatic fallout between Russia and Britain over Moscow's refusal to extradite Andrei Lugovoi, London's main suspect in the case, citing the Constitution.
Lugovoi, a former KGB operative who owns a multi-million dollar private security firm, was elected to Russia's parliament in December last year, as a member of the ultra-nationalist Liberal Democratic Party. His status as a lawmaker gives him immunity from prosecution in Russia.
