Ten days after Alexander Litvinenko succumbed in a London hospital to poisoning by highly radioactive polonium-210, the mystery surrounding the death of the former Russian agent has merely deepened.
The affair has drawn in the Kremlin and its security services, Russian exiles in Britain, and reports of radioactive traces being found not only in London but on aircraft plying the Moscow route. Only yesterday a Finnair jetliner tested positive in the Russian capital. But in an exotic cast of characters, nobody is more mysterious than Mario Scaramella, the self-styled Italian "professor" who lunched with the Russian defector on the day he was poisoned.
It was at the Itsu sushi bar in Piccadilly, where the two men met at 3pm on 1 November, that the highest levels of polonium-210 radiation have been found. Mr Scaramella says he only drank water, while Mr Litvinenko had miso soup and sushi. Traces of the radioactive substance have also been found in the Millennium Hotel in Grosvenor Square, where the defector had tea with Russian associates, including a former colleague in the FSB, the successor service to the KGB, later in the afternoon.
And Mr Scaramella himself has now tested positive for the deadly isotope, and is being treated at University College Hospital, where Mr Litvinenko died. Mr Scaramella is not said to be in danger, but somehow or other he came into contact with the substance.
Mr Litvinenko accused Mr Scaramella of poisoning him from the day he first fell ill: as the Italian told me, his name was all over Russian and Chechen websites as the main suspect in the poisoning of the former FSB agent long before the story hit the British press. Mr Litvinenko retained his suspicion right up to his death. Speaking of the Itsu meeting, he said: "Mario didn't want anything, he gave me the email printouts ... I said to myself, he could have sent these emails by computer. But instead he wanted to come and give them to me in person: why, and why in such a hurry? He was very nervous."
Mr Scaramella told me that he wanted to hand over the emails in person, because their contents were so sensitive. He said that he told the Russian at the restaurant: "You introduced me to [former Russian spy] Yevgeny Limarev, now Limarev has sent me a very strong statement."
The emails, which The Independent on Sunday has seen, stated that " Russian intelligence officers speak more and more about the necessity to use force" against Mr Scaramella and Mr Litvinenko, among others. But Mr Limarev has denied sending the emails, and his name does not appear anywhere in them.
British police have said they do not consider Mr Scaramella a suspect in Mr Litvinenko's death. He flew to London again last week to meet detectives voluntarily, and the two bodyguards keeping an eye on him at University College Hospital are there for his protection. Since being named as Mr Litvinenko's murderer in the Chechen press, he told me, his life has been at risk. "I was told, if you touch Mr Litvinenko, the Chechens will kill you," he said. "The Chechens have identified me as a military target." Mr Litvinenko was a strong supporter of the Chechen cause after defecting to the UK in 2001.
But while Mr Scaramella's problems in Britain may be mostly medical, in Italy last week he found himself at the centre of a criminal investigation. The accusations date from the five years when he was a consultant to the Mitrokhin Commission, an Italian parliamentary body set up in 2001 on the orders of the then Prime Minister, Silvio Berlusconi, to investigate the activities of Soviet and post-Soviet spies in Italy.
Mr Scaramella claims to be many things, including a professor at Naples University, an honorary magistrate, and consultant to something called the Environmental Crime Protection Programme (ECPP). But Naples University has not heard of him. The ECPP has no fixed office. The post as magistrate is non-paying. The only job he has had in recent years over which there is no doubt is with the Mitrokhin Commission.
Yet it is this job, which finished before Italy's general election in April, that has now landed him in hot water. On the orders of the public prosecutor of Naples, Mr Scaramella's phone was tapped; last week Italian papers published what were reported to be transcripts of conversations between him and the president of the Mitrokhin Commission, Senator Paolo Guzzanti, a member of Mr Berlusconi's Forza Italia party.
The transcripts allegedly show the two men discussing how Mr Scaramella is to acquire strong enough evidence from Moscow to label Romano Prodi, then the leader of Italy's centre-left opposition, now Prime Minister, a tool of the Russians. Other members of the Prodi government were also said to have been targeted, including the head of the Green Party, Alfonso Scanio, who is now environment minister.
"We can't go so far as to say Prodi is a KGB agent," Mr Scaramella allegedly says at one point. "But we can say that the Russians consider Prodi a friend ..." Mr Guzzanti explodes. "Friend doesn't mean a fucking thing!" he roars. "Are you taking me for a cunt?"
Lawyers for Mr Scaramella and Mr Guzzanti have protested at the bugging, but have not questioned the authenticity of the transcripts. After they appeared, Mr Prodi announced that he would sue "all those who, by words and deeds, have wounded my dignity as a citizen and as a representative of institutions".
Doubts about Mr Scaramella's work for the Mitrokhin Commission are not new. In 2004, opposition members of the commission described his contributions as "barely credible and not at all helpful ... grotesque and mysterious ... " But yesterday Oleg Gordievsky, the most senior Russian agent ever to defect to Britain, said Mr Scaramella's main source for allegations against Mr Prodi was none other than Mr Litivinenko, who came to this country in 2000 and recently became a British citizen.
"I was with Litvinenko when we met members of the UK Independence Party, " Mr Gordievsky told the IoS yesterday. "He told them that a KGB general, Anatoly Trofimov, had said to him: 'Prodi is one of ours.' The UKIP members later repeated the allegation in the European Parliament, when Mr Prodi was head of the European Commission in Brussels."
Mr Gordievsky, who was smuggled to Britain by MI6 after coming under suspicion as a double agent in 1985, said he knew nothing to support the allegations against Mr Prodi. But he was at one with Mr Litvinenko's other associates in accusing the Kremlin of murdering him. "Since July Russia has had a law permitting the FSB to kill people abroad that it doesn't like," he said. "They killed a British citizen on British soil, and they are smearing other people, including me."
The death of the former FSB agent is an undoubted embarrassment to Britain's security services, amid suggestions that they relaxed their guard once he had been in the country for a few years. But one well-connected source claimed the investigation into the affair showed there were wider implications. He speculated that Mr Litvinenko's poisoning could have been an accidental by-product of a terror plot involving radioactive material, and directed against Russia.
But the more the affair is discussed, the murkier it becomes. Nuclear experts insist that only a state would have the resources necessary to produce the polonium-210 used in the killing. One source said that officials from the International Atomic Energy Agency (IAEA) had helped investigators identify the Russian reactor where the polonium used to kill Mr Litvinenko was produced. In Russia, the source, added, security is not tight around Russian reactors. There would be plenty of highly qualified but poorly paid scientists with access to the material who could be tempted to obtain it on behalf of a criminal gang in return for money.
All this, however, does not answer the question: who killed Alexander Litvinenko? "All we have is a significant date of 1 November, because that is when Litvinenko became ill," said a Whitehall source. " According to the records, that is the first time that he called an ambulance. "
Scotland Yard is still working round the clock to plot the radiation trail, which appears to have spread not only round parts of England but also the world. Detectives are trying to work their way back to a "clean episode" where there is no radiation contamination. Only then can they establish when and where Mr Litvinenko came to ingest such a huge dose of polonium-210. They have not ruled out murder or suicide, but it is understood officers have ruled out a link between a reported firebomb attack on Mr Litvinenko's London home and his poisoning. His body suffered extreme trauma as a result of the level of radiation it received, but experts hope they can still establish the exact dose that he ingested.
But Whitehall is playing down any suggestion that the contamination of Mr Scaramella makes him a likely suspect. "It is unlikely for a major suspect to return to a crime scene and even more unlikely for them to voluntarily give police a debrief. This is being treated as a suspicious event, not as a murder inquiry," one source said.
Additional reporting by Sophie Goodchild, Raymond Whitaker and Francis Elliott
From Moscow to Rome: Some of Italy's leading figures have crossed Mario Scaramella's path
Set up the Mitrokhin Commission, which hired Scaramella as a consultant. The commission has been called a crude attempt to smear Berlusconi's opponents as communists
Now Prime Minister. Said to be the principal target of attempts to link Italian
politicians with the KGB. Among his accusers, according to another defector, was Alexander Litvinenko
Senator from Berlusconi's Forza Italia party and head of the Mitrokhin Commission. Phone transcripts allegedly show him using obscenities as he tells Scaramella to find more dirt on Prodi
Now environment minister and another alleged target of political smear campaign. Right, the front page of La Repubblica, carrying leaked transcripts of calls between Guzzanti and Scaramella
THE WIDOW: 'My love for my wife and son knows no bounds'
One of the few people to have remained silent since the death of Alexander Litvinenko is his widow, Marina, despite all the speculation, claims and counter-claims about who poisoned her husband.
Mrs Litvinenko, 44, was at the former KGB agent's bedside when he died on 23 November, and this week she faces the heartbreaking task of burying him in a specially sealed coffin.
In the long term, she also faces the possible impact of having been in close contact with her husband in the weeks leading up to his death. It is understood that she is the "family member" who has tested positive for small amounts of polonium-210, although health protection officials have refused to confirm this.
Mrs Litvinenko stayed with her husband as he lay dying in University College Hospital. The level of polonium-210 she has been exposed to is not thought to be dangerous, but it could increase her risk of cancer.
Those close to Mrs Litvinenko have said she repeatedly claimed that her husband had been deliberately targeted after a meeting with an underworld contact, but that medical staff had ignored her.
One is reported as saying: "She suspected from an early stage that her husband had been poisoned, but the hospital staff weren't taking her seriously. Had they tested for poison earlier, then maybe they could have done something to prevent him getting worse."
A day before his death, Mr Litvinenko paid tribute to her in a whispered statement: "I thank my wife, Marina. My love for her and our son knows no bounds."