Litvinenko, a former lieutenant colonel with Russia's federal security service (FSB) who had lived in Britain for six years, was apparently poisoned with the rare radioactive isotope polonium 210. This is tragic, shocking and mysterious. Yet, looking on from Moscow, the response in parts of the British press seems little short of hysterical.

Most worrying is the assumption that the Kremlin is bang to rights. In an editorial on Saturday, the Times argued that Vladimir Putin "must prove by deeds he is not linked to Litvinenko's murder".

Why must he? There is not a scrap of evidence to show that the Russian president was involved. Police are hardly out of the blocks and we're already up for some kangaroo justice.

Russia has killed people abroad, it is true, and recently. In 2004 two military-intelligence agents blew up the Chechen separatist leader Zelimkhan Yandarbiyev in Qatar (the Americans helped). That was wrong, but Yandarbiyev was a real threat, channelling funding to militants on Russian soil. Litvinenko, however, was a spent force as a critic of Putin. Even in purely pragmatic terms, the notion that the president would order his murder in Britain on the eve of an EU-Russia summit seems unlikely.

Naturally, I'll be the first to eat my shapka if Putin turns out to be to blame. The siloviki - the security-service veterans around the president - may have killed Litvinenko as a shot across the bows of competing clans.

There is a possibility that rogue elements are at work in the security services, or that Litvinenko was murdered for acquiring damaging evidence about the assassination in Moscow last month of the investigative reporter Anna Politkovskaya (although her colleagues at Novaya Gazeta doubt that). Of course, not being in control of the FSB is a potentially more damaging indictment of Putin than having sent a note to its boss, Nikolai Patrushev, saying "get Litvinenko". But we need to recognise that there are other actors in this drama besides our latest favourite tyrant.

The idea that Litvinenko was a crusading dissident in the mould of Alexander Solzhenitsyn is risible. People who had never heard of him two weeks ago are now trumpeting his "courageous, high-profile stand against the Kremlin". The fact is that Litvinenko was a paid employee of Boris Berezovsky, the oligarch and archenemy of Putin.

Berezovsky and Litvinenko, who both fled Moscow for Britain in 2000, first met in 1994. Litvinenko, as a serving FSB officer, was investigating a car bombing that decapitated Berezovsky's driver and narrowly missed killing the businessman. At the time there were many vicious fights between criminal clans in Moscow. By his own admission, Litvinenko worked in an FSB unit that planned extrajudicial killings.

Berezovsky and Litvinenko's relationship was forged in this atmosphere. By then, Berezovsky, a car dealer and multimillionaire, had penetrated the Kremlin and was pulling the strings. But his power began to slip and his business dealings fell under suspicion. In this context, the appearance of Litvinenko at a press conference in 1998 claiming his FSB bosses had ordered him to kill Berezovsky looked more like a clever political ruse than heroic whistleblowing.

Similar suspicions arise today. A familiar band of Russian malcontents have been feeding us with apocalyptic quotes for more than a week.

Unfortunately, radioactive isotopes like the polonium 210 that killed Litvinenko are available on the international black market, not only to special services. It is entirely plausible that a powerful foe whose path Litvinenko crossed in the dark, internecine fights of the late 1990s has crawled back and exacted revenge. That would be a sad reflection of today's Russia, but it would not be "state-sponsored terrorism".

Under President Putin "there have been huge attacks on individual liberty and on democracy. And it's important that he retakes the democratic road, in my view."
His remarks came as the Conservatives sought a Commons statement today from the home secretary, John Reid, on the safety of Russian citizens in the UK following the death of Mr Litvinenko weeks after he was poisoned by radioactive polonium 210.

Although police are resisting calling their investigation a murder inquiry, senior MPs are openly using the term. The shadow defence secretary, Liam Fox, said it was unacceptable for any UK citizen to be murdered inside their own country, while the Foreign Office minister Kim Howells has reportedly spoken of a naturalised British citizen "murdered on British streets by foreign nationals".

The Liberal Democrat leader, Sir Menzies Campbell, said the government should have been "much tougher" on Mr Putin and relations would have to be considered carefully if Mr Litvinenko's death was found to be the result of "state terrorism".

The government is trying to avoid making a Commons statement today, saying the issue is best left as a police matter. Mr Reid said the police have said they regard the death as suspicious and are keeping all options open.

But, speaking on the BBC AM programme, Mr Hain said the recent events were "casting a cloud over President Putin's success in binding Russia together and in achieving economic stability out of chaos that he inherited".

Mr Hain's remarks were unusual in voicing widely held private concerns in government. Senior Foreign Office ministers have been warning for a week that they dreaded the death of Mr Litvinenko because it was likely to lead to an inquest and a police investigation that may find Russian secret services were implicated.

Anglo-Russian relations, and EU-Russian relations, have been in long-term decline, leading to a standoff over plans to negotiate a new comprehensive treaty between Russian and the EU to replace the one due to expire at the end of 2007.

The EU has also been pressing for years for the liberalisation of access to Russian gas pipelines and greater opportunities for European oil companies to invest in the country. Russia, aware that its energy superpower status is the way back to a wider world role after the collapse of the Soviet Union, has been increasingly hostile to calls for liberalisation and feels it has been barred from buying into energy distribution companies in the west.

Tony Blair's support for a new generation of nuclear power stations, and signing of energy deals with Norway are in large part prompted by concerns over British energy security and becoming over-dependent on Russian oil and gas. A recent bulletin from the Centre for European Reform thinktank noted: "While energy experts are less concerned about Russia's willingness to sell energy to Europe, they worry greatly about its ability to do so. Oil output growth in Russia has dropped off sharply at a time of record oil prices. Similarly, Russia's gas output has been flat for years."

At the beginning of the year, the dominant view inside No 10 was that Mr Putin could be readily managed so long as he was shown respect. There is now a feeling that something more sinister may be happening in Russia, and Mr Putin is taking the country on irreversible course away from democracy.

A Chechen separatist leader claimed yesterday that Mr Litvinenko's death was a "form of terrorism" in the same vein as the July 7 bombings, and urged the British government to speak out. Ahmed Zakayev, a former actor who became the righthand man of the elected Chechen president, claimed that Mr Litvinenko was a victim of state-sponsored assassination, who had died fighting the Russian president.

"The death of Litvinenko - for Russia, for the security services - means nothing," Valery Dyatlenko said on state-run Channel One television, contending that neither the Kremlin nor Russia's intelligence agencies would have reason to kill him. "I think this is another game of some kind by Berezovsky."

Berezovsky amassed a fortune in dubious privatisation deals after the 1991 Soviet collapse and became an influential Kremlin insider under President Boris Yeltsin, but fell out of favour with Putin and fled to Britain in 2000 to avoid a money laundering probe which he said was politically motivated.

He has been a thorn in Putin's side for years, assailing him for backtracking on democracy and accusing Russian security services of organising the 1999 apartment block bombings that helped stoke support for the Chechen war.

That claim can be seen as aimed personally against Putin, a former Federal Security Service chief who ascended to the presidency in part on the strength of the popularity of his hardline stance on Chechnya as Prime Minister at the time.

Berezovsky provided financing for a book Litvinenko co-authored detailing the alleged bombing conspiracy, but their names had been linked since 1998, when Litvinenko publicly accused his superiors at the Federal Security Service, known by its Russian acronym FSB, of ordering him to kill Berezovsky.

Both men lived in Britain and Berezovsky, who spent time by Litvinenko's hospital bedside, has said he suspected Russia's intelligence services were behind the alleged assassination attempt.

But in Russia today, pro-Kremlin lawmakers suggested Berezovsky was behind the poisoning.

"Possibly there was a conflict," Nikolai Kovalyov, an MP and former FSB director, said on Channel One television. "In untying this knot called the relationship between Berezovsky and Litvinenko, it was necessary to receive the maximum benefit - and the benefit here for Boris Abramovich (Berezovsky) is ... the accusation of Russia's involvement in the killing."

Litvinenko had close ties with "certain oligarchs, including Mr Berezovsky, who in recent years have been deprived of the chance to buy corrupt power with stolen money and apparently cannot accept this", said Konstanin Kosachev, head of the foreign affairs committee in the State Duma, the lower House of Parliament.

"It's clear we may be talking about a targeted action aimed against modern Russia," Kosachev, a member of the dominant Kremlin-controlled United Russia party, whose comments often reflect the governments' stance. said on Channel One.

The remarks echoed Sergei Yastrzhembsky, Putin's chief envoy to the European Union, who named no names but suggested to reporters in Helsinki that someone was killing government critics to discredit the Kremlin. "I am far from being a champion of conspiracy theory. But it looks like we are facing a well-orchestrated campaign or a plan to consistently discredit Russia and its leader," he said.

Putin and other top Russian officials have repeatedly made hints of forces in the West that are out to undermine Russia.

After the murder last month of Russian journalist Anna Politkovskaya, a fierce critic of the war in Chechnya, Putin said that "people who are hiding from Russian law enforcement have been hatching plans to sacrifice someone and create an anti-Russian wave in the world" - a possible reference to Berezovsky.

Russian prosecutors said earlier this year that they had filed a new request for Berezovsky's extradition from Britain after charging him with planning a violent seizure of power.

SMERSH, a Russian acronym for "Death to Spies," was created by the Soviets in the 1940s to liquidate enemy agents and defectors.

It reported directly to Stalin. SMERSH and the NKVD/KGB's "Special Tasks" unit assassinated Ukrainian and Baltic nationalist leaders.

The favoured weapons of Soviet "wet affairs" units were undetectable poisons developed by Moscow's top secret "Lab X" that made victims appear to have died from natural causes. Lab X was founded in 1937 and continues, as "Laboratory 12," to this day. The CIA had its own version.

Ukraine's nationalist leader Viktor Yushchenko, Chechen independence fighter Khattab, and now Litvinenko, were all victims of untraceable poisons. PLO leader Yasser Arafat may have been a victim of a similar toxin.

A Bulgarian dissident, Georgi Markov, was poisoned in London in 1978 by means of an umbrella that drove a tiny poison bead into his leg. The secret files of Bulgaria's intelligence service -- which often performed "wet affairs" for KGB and remains under suspicion in the attempted assassination of Pope John Paul II -- are shortly due to be opened. Three senior archivists of these files have "committed suicide," two recently.

The Litvinenko affair is incredibly murky and just as fascinating. To understand it, go back to 1989.

As the Soviet Union began crumbling, I was the first western journalist given access to KGB's top brass, headquarters, and archives. "KGB is a powerful force behind modernization and reform," I reported from Moscow that year, adding that the KGB's best and brightest officers from the elite First Chief Directorate had decided to abandon the communists and seize control of business and government.

A 'Russian Pinochet'

The First Directorate's agents, including up-and-comer Vladimir Putin, were Russia's best educated, most sophisticated, and disciplined citizens. They knew communism had wrecked Russia. KGB chiefs told me in 1989 they wanted a "Russian Pinochet," a strongman who would bring in capitalism and make Russia and Russians work.

Today, two decades later, former KGB officers run the Kremlin, Russia's government, and much of its industry.

As the USSR collapsed, a group of sharp-minded financial opportunists called "oligarchs" grabbed control of itsindustries and resources.

Led by Boris Berezovsky, they formed the core support for Boris Yeltsin' s stumbling regime -- with huge amounts of covert U.S. finance.

KGB -- divided in 1991 into the foreign SVR and internal FSB51 -- viewed Berezovsky and other oligarchs as traitors and foreign agents

Also in 1991, the Chechens, a Muslim Caucasian mountain people who had battled Russian colonial rule for 300 years, demanded independence from Russia, similar to its other former republics. Berezovsky backed their calls.

In 1994, Yelstin provoked a war and sent his army to crush Chechen independence. Savage Russian bombing and shelling killed up to 100,000 Chechens.

In a military miracle, Chechen fighters defeated Russian forces in two years of bitter fighting and drove them out. In 1997, Yeltsin signed a peace treaty granting Chechnya independence.

Vowed revenge

But the "siloviki" -- Russia's security and military apparatus -- wereoutraged and vowed revenge. Yeltsin was discredited as a drunken buffoon. At the end of 1999, he was ousted by a discreet coup that made then little-known prime minister, and former KGB officer,Vladimir Putin, president of Russia.

During 1999, Moscow and a provincial city were racked by a series of apartment building bombings that killed 300 people. Panic swept Russia.

The bombings were blamed on "Chechen Islamic terrorists." But Moscow police caught a team of SVR agents red-handed planting explosives in a residential building. The agents claimed they were running a "security test."

This awkward fact was hushed up. Putin called for total war "to wipe out Chechen terrorism" and "kill them in their outhouses." Outraged Russians rallied behind Putin, giving him a huge electoral mandate in 2000. Putin sent his army to invade and re-conquer Chechnya.

The parallels to the 9/11 attacks on America a year later were uncanny.

Lt. Col. Alexander Litvinenko wrote a book about the apartment bombings and claimed his own agency, FSB, was behind them. The book was financed by Berezovsky, who had emerged as Putin's main rival for power. In 1998, Litvinenko publicly claimed the secret police planned to kill Berezovsky.

Litvinenko was jailed, then fled into exile in Britain. Berezovsky, charged with fraud, later followed him to exile in London where he continues plotting to overthrow Putin.

Journalist murdered

Shortly before Litvinenko was poisoned, he was investigating last month's murder in Moscow of crusading Russian journalist Anna Politkovskaya.She had courageously exposed Russian criminality and rights abuses in Chechnya. Politkovskaya told me she was marked for death by "silovoki" and Russian gangsters.

Litvinenko and Berezovsky accused Putin of authoring Politkovskaya's murder. The Kremlin strongly denied any involvement, or any role in Litvinenko's poisoning.

Both crimes have further damaged Russia's image, and tarnished President Putin's image as a strong but law-abiding leader. Yet one must wonder why the Kremlin would risk igniting such a storm to silence a minor figure whose accusations went largely unheeded.

Perhaps thin-skinned officials in Moscow reverted to old Soviet ways by dispatching the "Smershniki."

The Kremlin blames a feud among Russian exiles. But the blood spots connect right to Moscow. One feels a chilly breeze from the days of the Cold War.

This was six years ago. Berezovsky's subsequent role in Litvinenko's life - as Litvinenko's in his - is shrouded in the mystery that obscures so many exiled Russian plutocrats. But there is evidence that they kept up at very least what might be called a business relationship. Berezovsky sponsored a book that Litvinenko published in 2003, supposedly lifting the lid on the murkier doings of the FSB. If, as has been said, Litvinenko was investigating the contract-killing of the Russian journalist Anna Politkovskaya at the time he fell ill, this is likely to have been at Berezovsky's instigation, too. Berezovsky is reliably reported to have been at Litvinenko's bedside on the day the media were first made aware of his illness.

While a personal friendship may have grown up between the two men, Litvinenko had contacts and information that could have been of great help to Berezovsky. As an agent through the years of Vladimir Putin's rise to the Russian presidency, he claimed to know where many bodies were buried. And anything that besmirched Putin was grist to the mill of Berezovsky, who aspired to lead an organised opposition to Putin from abroad.

The origins of Berezovsky's venom against Putin go back a decade. Then in their 40s, the two men were highly competitive Kremlin wannabes, vying for influence at President Boris Yeltsin's court. Berezovsky had a head start, ingratiating himself into Yeltsin's inner circle - the so-called "family" - by dint of his money and connections. Seen as the original oligarch, he was already the richest and most influential of Russia's new tycoons, a compulsive networker with fingers in many pies.

His influence was at its most valuable to Yeltsin in 1996. Six months before the scheduled presidential election, Yeltsin's popularity ratings stood at a catastrophic 30 per cent. His chief rival was the far-right nationalist Vladimir Zhirinovsky, who was well placed to beat him. Berezovsky deployed his money and influence lavishly, forming a group of oligarchs, the "Big Seven", to underwrite Yeltsin's campaign. They media outlets they then owned were dedicated to a schedule of "all Yeltsin all the time".

The voters gave their President another four years. The West breathed a sigh of relief, and Berezovsky reaped his reward. Initially it was the mostly honorific post of deputy secretary of the National Security Council, then secretary of a Kremlin group co-ordinating the so-called Commonwealth of Independent States - the body trying to maintain economic and political links between the states of the former Soviet Union.

As Berezovsky tells it, it was during this time that he conducted peace negotiations - often secretly - with rebellious Chechnya. His first-hand dealings with Chechen leaders left him with an enduring sympathy for this mountain people and their seemingly doomed quest for autonomy. Until recently, he claimed still to be involved in efforts to forge a settlement.

By 1998, Berezovsky's star at the Kremlin was fading, just as Vladimir Putin's started to shine bright. With Yeltsin not standing for election again, Berezovsky's services as media Svengali and chief financier were less in demand. The currency crash of that year prompted public questions about the oligarchs' fortunes. Berezovsky left Yeltsin's entourage the following year.

He decided to try his luck as a front-line politician, and was duly elected the member of parliament for Karachayevo-Cherkessiya, a region not only close to Chechnya, but also one where money talks. An additional advantage of this move was the immunity from prosecution a Duma seat afforded. He may have calculated that for four years he would be safe.

At the same time, Berezovsky had to watch as the ailing Yeltsin relied more and more on Putin. Berezovsky had become seriously disenchanted with Putin, a man with whom five years before he had been on skiing terms. He now saw Putin as a sporty little upstart from St Petersburg who was applying his second-rate secret agent's brain to keeping the precarious Russian government functioning.

At the end of 1999, it was Putin who was anointed by Yeltsin as his successor. Berezovsky was cast aside. All his hard work trying to solve the Chechen problem had been negated by a war he believed Putin had begun as an election ploy. Threatened with prosecution for fraud in connection with his holdings in the state airline Aeroflot and the privatised state car company, Logovaz, he made one of his many visits to London permanent.

That this stubborn and scheming tycoon chose exile was perhaps a less unlikely outcome than the fact that he had come so close to power at all. A congenital outsider, Berezovsky was able to turn to his benefit the brief period of extreme social and political mobility that followed the break-up of the Soviet Union. Born in Moscow into a modest Jewish family, he was academically ambitious, but thwarted in his first choice of study - space science - by the restrictions on the numbers of Jewish students in certain faculties. After a series of junior research positions, he finally obtained a doctorate in computer science at the age of 37.

He was 40 when Mikhail Gorbachev came to power and the political landscape began to change. In 1989 - ahead of most - he sensed the way the wind was blowing and made the leap into business. And questionable business some of it was, too. As he tells it, he built his fortune on a couple of second-hand Mercedes cars he bought in what was then East Germany, which he resold at a large profit in Russia.

But the myth that has grown up around him is replete with hair-raising stories of hijacked trains, nocturnal visits to car assembly lines in southern Russia, secret cash deals, all liberally spiced with armed thugs and unexplained disappearances. A risk-taker par excellence, Berezovsky thrived in the volatility of those years, amassing a fortune that took him from cars into oil, aluminium and property and - as his weapon in what he anticipated would be the battles ahead - into television and newspapers.

His lifestyle - with its fast cars, servants, a palatial residence outside Moscow and vicious guard dogs - was the stuff of legend. His renown was such that a Russian director made a film, Oligarch, apparently based on his adventurous life. It was released in 2002, and drew gasps from Russian audiences for the private opulence it showed.

Before leaving Moscow for what he hoped in 2000 would be temporary exile, Berezovsky formed an opposition party, Liberal Russia, intended to unite leading businessmen and other devotees of a free market who felt that their interests were threatened by Putin. The party was plagued with splits and petered out. But politics - or more correctly, perhaps, politicking - remains Berezovsky's passion. He may be sustained financially in London by his extensive property portfolio and his oil interests, but it is opposition politics that is his true lifeblood.

He works out of an office in Mayfair that is imbued with a faint air of menace. A slight man, with features somewhat reminiscent - ironically - of Lenin, he employs large, surly bodyguards, a fleet of black-glassed 4x4s, reputedly armour plated, and commutes into town from his country estate in Surrey. He claims that the Russian authorities have tried to kill him at least three times and he is careful about public appearances. He travels mostly in convoy, altering his route and his drivers and speeding with apparent impunity.

He has been progressively shorn of his media interests in Russia. He sold his controlling stake in the Kommersant newspaper earlier this year, prompting speculation that he might need the money. His official political vehicle in Britain is a group curiously called the Civil Rights Foundation, which he seems to do little publicly to promote, but may channel money to opposition groups in the former USSR. Berezovsky boasted that he had funded Ukraine's Orange revolution.

If his attempts to foment revolution in and around Russia have so far failed, however, Berezovsky was hugely successful in insinuating himself into the clubs and salons of London. Suave and charming, he was lionised as a successful and wealthy opponent of the present regime in Russia. Always ready with flashy quotes, always game to appear on platforms to denounce his arch-foe, Vladimir Putin, he has proved almost as masterly an image-maker in his adopted country as he was in Russia. A Channel 4 documentary this year suggested he was singlehandedly responsible for the negative image of Putin's Russia that prevails among Britain's chattering classes.

There are signs, though, that his power is waning. His ability to mesmerise the great and good went into decline after the Chechen attack on Beslan. He is not confident enough in English to dominate a platform alone. And earlier this year, the then foreign secretary Jack Straw took the unusual step of warning him publicly that he must cease to advocate the violent overthrow of Putin or risk forfeiting his refugee status.

Russia would dearly love to get its hands on Berezovsky. Even after six years away, in Russia his name is still synonymous to many with the great privatisation swindle of the 1990s. And Putin would surely see his downfall as a personal triumph. Berezovsky, though, for all his scheming is a shrewd and cautious survivor. He keeps at arm's length from the action - a puppeteer invisibly pulling fewer and fewer strings.

A Life in Brief

BORN 23 January 1946, in Moscow.

FAMILY Six children by four marriages.

EDUCATION 1968: graduated from Moscow forestry engineering institute; 1983: doctorate in computer science, Moscow State University.

CAREER 1969-87: research fellow, Russian Academy of Sciences; 1989: used car business; 1992: buys into oil company Sibneft; 1995: buys into ORT; 1996: joins Yeltsin's re-election campaign; 1999: elected to Duma; 2000: sets up Liberal Russia party but, facing charges of embezzlement, flees to London; 2003: granted political asylum in Britain.

HE SAYS "I am very bad at understanding people. I don't know who is a traitor, who is good, who is bad. But I'm good at understanding process."

THEY SAY "He is not an easy person to work with because of his impulsive character and short attention span... But he is a phenomenon." - Alex Goldfarb

Last night the Foreign Office said that officials had met with the Russian ambassador in London and had asked the Kremlin to hand over any information that it had which could help the Scotland Yard investigation.

Cobra, the Cabinet's emergency security committee, met yesterday after toxicologists confirmed that the 43-year-old former KGB colonel had a large dose of alpha radiation in his body. The committee chaired by John Reid, the Home Secretary, considered the risk to the public after the discovery of radioactive material in a Central London sushi bar and at the Millennium Hotel, near the US embassy in Grosvenor Square, where Mr Litvinenko held meetings on November 1. Radioactive traces were also found at his family home in Muswell Hill, North London.

The quantity of polonium-210 used could only have been obtained from a nuclear instillation, scientific experts said.

A senior Whitehall official said: "Cobra met because thousands of people have passed through the sushi bar in the past three weeks and there is a potential risk for the public and we have to examine all the implications."

Experts from the Government's Health Protection Agency tried to allay public fears by stressing that it was unlikely that friends, family and medics who were with Mr Litvinenko at University College Hospital had been contanimated.

Security sources said that MI5 and MI6 were engaged in a "joint enterprise" with Scotland Yard in what was "an unprecedented death" in Britain. Anti-terror squad Continuedetectives refused to say where the deadly element was placed, or in what quantities they found it at the Itsu sushi bar in Piccadilly or the Pine Bar of the Millennium Hotel, where the dissident met two Russians on November 1.

Mr Litvinenko's father, Walter, openly accused the Kremlin of murdering his son. They also released a statement that Mr Litvinenko dictated 48 hours before he died, blaming President Putin for his death.

Mr Litvinenko told the Russian President: "You may succeed in silencing one man, but the howl of protest from around the world will reverberate, Mr Putin, in your ears for the rest of your life.

"May God forgive you for what you have done, not only to me, but to beloved Russia and its people."

Mr Putin interrupted preparations for an EU/Russia summit in Helsinki to deny involvement. He criticised Mr Litvinenko's entourage, the media, the British secret service and even the Italian Mafia. He claimed that the letter accusing him of being "barbaric and ruthless" was a forgery concocted by Mr Litvinenko's wife and father: "If this note was produced before the death of Mr Litvinenko, I wonder why it was not published when he was alive?"

Mr Litvinenko's funeral will be held in London.

The former Soviet Union reportedly used polonium in its space program in the 1970s, and it is used also in devices designed to eliminate static electricity.

Polonium is so exceedingly rare that only about 100 grams is believed to be produced each year, said Dr. Mike Keir, a radiation protection adviser at Royal Victoria Infirmary.

"Only a very, very small amount of this would need to be ingested to kill," Keir said. "Unless you can remove the material, there's very little you can do except treat the symptoms."

Given his symptoms -- including hair loss, organ failure and immune system breakdown -- experts said that earlier hypotheses, such as thallium poisoning, were reasonable.

"Trying to identify the exact agent that was making him sick was like looking for a needle in a haystack," said Dr. Alistair Hay, a professor of environmental toxicology at Leeds University. There are numerous toxins capable of causing such serious damage without being immediately identified in the body, he said.

The alpha rays emitted by polonium are extremely hard to detect, and a fatal dose of the element may have rapidly penetrated his bone marrow without raising immediate suspicion. Earlier this week, doctors said Litvinenko was in need of a bone marrow transplant.

"As a result of alpha ray radiation, there are very clear genetic changes in the body," Keir said. "But to know for certain that it was polonium radiation, you need to actually find polonium particles," he said.

Polonium occurs naturally in very low concentrations in the Earth's crust, and was first discovered in 1898 by Nobel prize winning chemists Marie and Pierre Curie, as they were searching for the cause of radiation decay in uranium. They named it polonium in honor of her country of origin, Poland.

The world public is shocked. Nobody can understand why the Russian president did such a strange thing as kissing the stomach of an unfamiliar small boy.

The explanation may be found if we look carefully at the so-called "blank spots" in Putin's biography.

After graduating from the Andropov Institute, which prepares officers for the KGB intelligence service, Putin was not accepted into the foreign intelligence. Instead, he was sent to a junior position in KGB Leningrad Directorate. This was a very unusual twist for a career of an Andropov Institute's graduate with fluent German. Why did that happen with Putin?

Because, shortly before his graduation, his bosses learned that Putin was a pedophile. So say some people who knew Putin as a student at the Institute.

The Institute officials feared to report this to their own superiors, which would cause an unpleasant investigation. They decided it was easier just to avoid sending Putin abroad under some pretext. Such a solution is not unusual for the secret services.

Many years later, when Putin became the FSB director and was preparing for presidency, he began to seek and destroy any compromising materials collected against him by the secret services over earlier years. It was not difficult, provided he himself was the FSB director. Among other things, Putin found videotapes in the FSB Internal Security Directorate, which showed him making sex with some underage boys.

Interestingly, the video was recorded in the same conspiratorial flat in Polyanka Street in Moscow where Russian Prosecutor-General Yuri Skuratov was secretly video-taped with two prostitutes. Later, in the famous scandal, Putin (on Roman Abramovich's instructions) blackmailed Skuratov with these tapes and tried to persuade the Prosecutor-General to resign. In that conversation, Putin mentioned to Skuratov that he himself was also secretly video-taped making sex at the same bed. (But of course, he did not tell it was pedophilia rather than normal sex.) Later, Skuratov wrote about this in his book Variant Drakona (p.p. 153-154).