By Tristana Moore
BBC News, Berlin
The Litvinenko affair has reached Germany and with every day there is another twist to this mysterious story.
German police say there is no risk to the public
The German media have been gripped by the unfolding drama.
"Polonium Alarm," one newspaper headline ran. "More radiation victims" said another, as investigators continue to follow a radioactive trail around Hamburg left by the Russian businessman Dmitry Kovtun.
Four people linked to Mr Kovtun, his former wife, her two children and her partner are still in hospital suspected of being contaminated with polonium-210.
Police have found traces of the radioactive substance at a flat in Hamburg owned by Mr Kovtun's former wife.
Detectives believe the Russian businessman spent two nights in this apartment before flying to London to meet Alexander Litvinenko.
'The Third Man'
Further traces of polonium-210 were discovered in a car which picked up Mr Kovtun from Hamburg airport, on a document which was left at the immigration office in Hamburg and in the house belonging to the mother of Mr Kovtun's ex-wife in Haselau, west of Hamburg, which he also visited.
All locations have now been sealed off and radiation experts are at the scene.
"There is absolutely no risk to public health," said Andreas Schoepflin, a spokesman for Hamburg Police.
German police have set up a special taskforce aptly called "The Third Man" - a reference to the Cold War film directed by Carol Reed - and a British detective from Scotland Yard is helping with the inquiry.
Investigators have pieced together Mr Kovtun's last known movements in Hamburg in the four days prior to his trip to London on 1 November, when he met Alexander Litvinenko at the Millennium Hotel.
"We assume that Mr Kovtun arrived in Hamburg on 28 October on a flight from Moscow and that he was already contaminated with polonium-210," Martin Koehnke, Hamburg's chief prosecutor told the BBC.
Mr Kovtun met Alexander Litvinenko in London on 1 November
It appears that as soon as Mr Kovtun stepped off the plane at Hamburg airport, he started spreading the radioactive substance.
German prosecutors have opened a criminal investigation against Mr Kovtun on suspicion of illegally handling radioactive material.
"Dmitry Kovtun may not just be a victim, but he could also be a perpetrator," said Martin Koehnke.
Prosecutors face many unanswered questions: who took part in the Litvinenko murder plot, what is the state of Mr Kovtun's health and where did the polonium-210 come from?
Tip of iceberg
According to reports, Mr Kovtun is in a clinic in Moscow, where he is being treated for radiation poisoning, but there are conflicting accounts of his health.
As the investigation widens, Hamburg prosecutors officially lodged a request for information on the Litvinenko case with the Russian authorities.
The Kremlin has denied any involvement in the death of Alexander Litvinenko, and the authorities in Moscow have insisted that they are co-operating with British investigators.
But some observers in Berlin are concerned about the long-term impact of the Litvinenko affair which transcends the Kremlin.
"The Litvinenko case shows that there are dangerous criminal elements in the former Soviet Union which are involved in the smuggling of radioactive material around the world," said Alexander Rahr from the German Council of Foreign Relations.
"This could just be the tip of the iceberg, part of a wider threat from Russian criminal groups."
Millions of Germans tune in each Sunday night to "Tatort," a police drama series on television.
Now it seems that they have a real-life thriller on home soil.