Hamburg, Germany ? Traces of the rare radioactive substance polonium-210 were found at a German apartment visited by a contact of fatally poisoned ex-spy Alexander Litvinenko – before the two men met in London, authorities said Sunday.

The polonium traces were found on a couch where Russian businessman Dmitry Kovtun is believed to have slept at his ex-wife’s Hamburg apartment the night before he headed to London for a meeting with Litvinenko last month, German investigators said.

Tests on traces of radiation at the apartment “clearly show that it is polonium-210,” Gerald Kirchner of the Federal Radiation Protection agency said at a news conference.

Investigators said Kovtun flew to Hamburg from Moscow with Aeroflot on Oct. 28 and departed for London on Nov. 1. That is the day when Kovtun and at least one other Russian met with Litvinenko at London’s Millennium Hotel – and when Litvinenko is believed to have fallen ill.

Traces of radiation also were found in the passenger seat of a car that picked up Kovtun from the Hamburg airport, on a document Kovtun brought to Hamburg immigration authorities and at the home of Kovtun’s ex-mother-in-law outside Hamburg – all from before the Nov. 1 meeting.

German prosecutors did not say whether they suspect Kovtun might have been involved in Litvinenko’s death. But they said they were investigating him on suspicion he may have improperly handled radioactive material.

Officials said that any connection between Kovtun and Litvinenko’s death would have to be investigated by British police. British police are treating his death as a murder.

Litvinenko, an ex-Russian agent and fierce Kremlin critic, died Nov. 23 after blaming Russian President Vladimir Putin for the poisoning. The Kremlin has denied involvement.

Kovtun reportedly is being treated in Moscow for radiation poisoning. Russian authorities have opened a criminal investigation into his poisoning, calling it attempted murder.

Kirchner, the radiation agency official, said it was possible Kovtun already could have been poisoned when he arrived in Hamburg and left behind traces through body fluids such as sweat.

Litvinenko met at the Millennium Hotel in London’s Mayfair neighborhood with Kovtun and former Soviet agent Andrei Lugovoi. Lugovoi has denied that the men were involved in the ex-spy’s death.

Meanwhile, Litvinenko’s widow said in interviews published Sunday that her late husband’s criticism of the Kremlin had antagonized his former secret service colleagues, and contended that Putin had created an atmosphere that “makes it possible to kill a British person on British soil.”

In her first interviews, Marina Litvinenko said she believed Russian authorities were behind the poisoning of her husband, who sought asylum in Britain in 2000 and obtained citizenship this year. Marina Litvinenko told Sky News in an English-language interview that her husband “openly went out from system and accused the system of killing people, of kidnap.”