The four Germans were linked to Dmitry Kovtun, a Russian who met Litvinenko in London on the day he is believed to have been poisoned with polonium-210, a radioactive isotope.
They were hospitalized on December 11 after traces of polonium were found at two flats in Hamburg where Kovtun had stayed before traveling to London for his meeting with Litvinenko last month.
Litvinenko died in London on November 23. Kovtun is said to have developed symptoms of radiation poisoning.
Britain, Russia, and Germany have all now opened investigations into the Litvinenko case. The head of the Russian office of Interpol, Timur Lakhonin, said the international police force has been asked to help coordinate investigations.
(compiled from agency reports)
Aleksandr Litvinenko: A Timeline
CLOAK AND DAGGER: A timeline of a murder case that unraveled after Andrei Litvinenko, a former Russian security officer and vocal Kremlin critic, dies on November 23, 2006, of poisoning by radioactive isotope polonium-210.
In a deathbed letter, Litvinenko blames Russian President Vladimir Putin for his death -- a claim Putin condemns.
Investigators center on two meetings in London that Litvinenko had described -- one in which he met with two Russians for tea in London, and another in which he met with a third Russian at a sushi bar.
Six months later, British prosecutors announce they have enough evidence to charge a Russian citizen -- one of the men who had met with Litvinenko for tea -- with the murder ...more...
MORE: Coverage in Russian from RFE/RL's Russian Service.