The international police agency, Interpol has joined the investigation into the poisoning death of former Russian agent Alexander Litvinenko. For VOA News, Tom Rivers reports from London.

Interpol's considerable resources are being thrown into the murder investigation that includes probes in Britain, Russia and Germany.

The international force is being tasked with improving the information flow between the three states and may become more involved if leads take the investigation further. 

In Germany, the focus has been on a Hamburg apartment where traces of radioactive polonium-210 have been detected.

It has been established that businessman and former Russian security agent Dmitry Kovtun spent the night there just four days before he met up with former Russian spy Alexander Litvinenko in a London hotel bar.

The four people who live in the apartment, including Kovtun's ex-wife, have been checked for radiation poisoning.  German health officials say the levels are so low that any danger to those individuals has been ruled out.

Meanwhile in Moscow, Russian prosecutors say Kovtun has developed symptoms of radiation poisoning, but this can not be independently confirmed.

Another key witness in Moscow, Andrei Lugovoi, was questioned by British detectives Monday in a hospital where he is undergoing tests for radiation contamination.

Lugovoi was at the same meeting with Kovtun and Litvinenko on November 1, the day Litvinenko said he first became ill.  Litvinenko died November 23.

In a further development, Russian prosecutors say they plan to send a team of investigators to London as part of its inquiry.

While Russia will not allow the extradition of any suspects to Britain, the door is open for prosecutors in Moscow to pursue charges there if that is how the case develops.

In London, radiation screening continues for those who visited the bar in the Millennium hotel on or around November 1.  At least seven members of staff have tested positive for traces of polonium-210.