The witness, Andrei Lugovoi, met four times with Litvinenko in London in the month before his death by radiation poisoning, including once on the day that Litvinenko fell ill.
Prosecutor-General Yury Chaika said on December 5 that any witnesses called by the British would by questioned by Russian prosecutors in the presence of the British detectives.
British authorities in London today said faint levels of radiation had been discovered at a sports stadium visited by Lugovoi.
Litvinenko's death sparked public-health concerns in London and police have been testing for radiation at a number of sites around the city.
(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.