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LONDON, England (CNN) -- British detectives investigating the death of the former Russian spy Alexander Litvinenko are now pursuing inquiries in both London and Moscow. CNN's The Briefing Room has compiled a guide to who's who in the spy scandal.
Alexander Litvinenko -- the spy
Litvinenko was a KGB agent for 18 years whose job was to fight organized crime and counter subversion. He came to Britain in 2000 after turning whistle blower on the FSB (the KGB's successor) and claiming he had been ordered to assassinate the oligarch Boris Berezovsky (see below.)
Like other dissidents in London he was a vehement critic of President Putin and vocal about Chechen politics. He wrote "Blowing up Russia: Terror from Within," in which he claimed FSB agents and not Chechen rebels carried out a bomb attack on a Moscow apartment in 1999 which killed 300 people.
He died in University College Hospital, London on November 23 from a massive dose of the radioactive material polonium-210. In a deathbed statement he blamed Putin for his death -- something the Kremlin has strongly denied.
Dmitri Kovtun, Andrei Lugovoi, Vyacheslav Sokolenko -- the business associates
German investigators on December 11 said it is unknown whether Russian businessman Dmitry Kovtun was involved in the poisoning, or a victim of it. He is reportedly being treated in Moscow for radiation poisoning.
Lugovoi says he and his business associates Kovtun and Sokolenko met Litvinenko at the Millennium Hotel on November 1 -- the day he was poisoned. The men say they were in London on business and to see a football match.
All three have protested their innocence, while Lugovoi told Britain's Sunday Times newspaper that they are being "framed" by the real culprit.
On December 11 it emerged that radioactive traces were found in the passenger seat of a BMW car that Kovtun rode in, on a document that he brought to Hamburg immigration authorities, and at the home of Kovtun's ex-mother-in-law outside Hamburg -- all from before the November 1 meeting.
Mario Scaramella -- the contact
An Italian security expert who was one of the last people to see Litvinenko alive.
He met the spy at a sushi bar in central London on November 1 to warn him that both their lives were in danger after reportedly uncovering evidence that the men were on a hit list.
Last week he also tested positive for polonium 210 but so far doctors say he is "well."
Alexander Goldfarb -- the friend
As Litvinenko lay dying in hospital, Alexander Goldfarb emerged as an unofficial spokesman for the spy and his family.
He is the executive director of the International Foundation for Civil Liberties in New York, which was set up by exiled Berezovsky in 2000.
He met Litvinenko in a Russian prison in the late 1990s when he was director of a George Soros-funded project to tackle TB in the penal system and Litvinenko was awaiting trial on charges of abuse of office.
Yuri Shvets -- former KGB agent
A former KGB agent living in the U.S. who says he has given police the name of a suspect he believes orchestrated the killing of Litvinenko. On Monday he confirmed he had been questioned by British police and the FBI.
Shvets was a KGB major between 1980 and 1990 during which time he worked under cover in Washington as a correspondent for the Russian news agency, Tass. He emigrated to the U.S. in 1993 and wrote a book about his experiences.
Goldfarb says that Shvets had played a key-behind-the-scenes role in bringing about the Orange Revolution of 2004 which swept Ukrainian president Viktor Yushchenko to power.
Boris Berezovsky -- the exiled oligarch
The colorful Berezovsky made his money during the Yeltsin years by taking control of many state assets from oil and car companies to property. He was part of the Yeltsin inner circle and led an extravagant lifestyle immortalized in the film, "Oligarch."
But when Putin came to power, Berezovsky fell out of favor and found his business activities under scrutiny. He fled to Britain in 2000 and was granted political asylum in 2003. His also saw the demise of his media ambitions after his stake in Russia's major television company ORT was sold, and his own TV6 channel was closed down.
Berezovsky and Litvinenko came to know each other in the aftermath of a failed assassination attempt on the oligarch in 1994. Litvinenko ended up later accusing the FSB of involvement in the conspiracy, a charge that severed his ties with the agency.The pair maintained contact once in Britain. Berezovsky is a fierce critic of Putin and sympathetic to the Chechen cause.
Yegor Gaidar -- the "poisoned" former Russian PM
The former Russian PM Yegor Gaidar fell violently ill while attending a conference in Dublin just days after Litvinenko's death. His daughter said her father had been poisoned and that his alleged poisoning was linked to the death of Litvinenko.
The British embassy in Moscow issued a statement saying it did not believe there was any link between the two cases. Doctors in Moscow say they do not know what caused his mystery illness.
Anna Politkovskaya -- murdered journalist
The investigative journalist dedicated her career to exposing human rights abuses. She was shot dead outside her flat in Moscow on October 7. No arrests have been made in connection with her killing.
She made her name reporting from Chechnya for Russia's liberal newspaper, Novaya Gazeta. She was the author of two books in English, "A Dirty War: A Russian Reporter in Chechnya" (2001), and "Putin's Russia" (2004).
Litvinenko was apparently investigating her murder.
Mikhail Trepashkin -- the convict
The former KGB agent is serving four years in a Urals jail for divulging state secrets. From behind bars he accuses the FSB of creating a hit squad to kill Litvinenko and other enemies of the Kremlin.
He wants to pass the information on to detectives.
Russia's prison service says the ex-agent will not be allowed to meet UK investigators.
Julia Svetlichnaja -- the Chechen expert
Svetlichnaja is London-based academic who is writing a book on Chechnya. She told told Britain's Observer newspaper that Litvinenko had hoped to involve her in an audacious blackmail scheme. She said Litvinenko told her he had contacts in the FSB who would supply him with explosive details on Russian oligarchs and Kremlin figures. He then planned to use the information to blackmail them and wanted Svetlichnaja to help him.
John Reid and Sergey Lavrov -- the politicians
The British Home Secretary John Reid has promised the investigation will be far reaching. He says the police will follow wherever this investigation leads inside or outside Britain. "The worst thing we can do is speculate," he said. "This isn't a game of Cluedo."
Russia's Foreign Minister Sergey Lavrov has warned that continued suggestions of Russian official involvement in Litvinenko's death could damage relations with Britain.