BERLIN, December 14 (RIA Novosti) - The ex-wife of Dmitry Kovtun, a witness in the case of a murdered former Russian security service officer, was released from a hospital in Germany Thursday along with her children and boyfriend, Kovtun's German lawyer said.

Medical tests did not reveal traces of radioactive polonium-210, the toxic isotope used to kill Alexander Litvinenko, the lawyer said.

German police have said Kovtun spent two nights at his ex-wife's home in Hamburg just before he met with Litvinenko in London on November 1, which Litvinenko believed to be the day of his fatal poisoning.

German authorities 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. Prosecutors are investigating the agent-turned-businessman, who has a German residence permit, on suspicion of illegally transporting radioactive materials.