London:
Shortly after the radiation poisoning in London of a former K.G.B. officer, Alexander V. Litvinenko, a senior Russian official asserted that Moscow had been tailing his killers before he died but had been waved off by Britain's security services, according to a cable in the trove of secret American documents released by WikiLeaks.
The Russian assertion, denied by British officials, seemed to revive a theory that the British intelligence services played a murky role in the killing -- a notion voiced at the time by some in Moscow to deflect allegations of the Kremlin's involvement in the murder.
The cable, dated Dec. 26, 2006, and marked "secret," was one of several in the WikiLeaks trove that tried to examine the still unanswered question of who exactly ordered the use of a rare radioactive isotope, polonium 210, to poison Mr. Litvinenko, leading to his death on Nov. 23, 2006.
Russia produces polonium commercially, but the process is closely guarded and British investigators have concluded that the isotope could not have been easily diverted without high-level intervention.
In a telephone interview, Marina Litvinenko, the widow of the former K.G.B. officer, called the Russian assertion "disinformation."
"When they prepared this, they never expected polonium would be known as a murder weapon," she said. "But after Nov. 23, they needed some kind of disinformation."
She said that "polonium could not be used without very high level" involvement of the security services.
A separate cable from Paris suggested that at least one senior American official, Daniel Fried, seemed skeptical of statements by Vladimir V. Putin -- then Russia's president and now prime minister -- that he was unaware of the events leading to the killing, which Britain has blamed on another former K.G.B. officer, Andrei K. Lugovoi.
Mr. Lugovoi, now a member of the Russian Parliament, has denied British charges that he murdered Mr. Litvinenko by slipping polonium into a teapot at a British hotel where the two men met on Nov. 1, 2006.
Russia has refused a British request for Mr. Lugovoi's extradition and the relationship between two countries has not fully recovered from deep strains after Mr. Litvinenko's death.
Among several cables mentioning the affair, perhaps the most sensitive covers a meeting in Paris on Dec. 7, 2006, between an American ambassador at large, Henry Crumpton, and Anatoly Safonov, at the time a special representative of Mr. Putin.
That encounter had a whiff of an espionage film script. The two met over a dinner described as "amicable." Both men were veterans of their countries' intelligence services, and were now assigned by their governments to cooperate in counterterrorism.
Mr. Crumpton had led the C.I.A.'s operation in Afghanistan after the Sept. 11, 2001, attacks. Mr. Safonov was a former K.G.B. colonel-general who had risen to high office as deputy director in its successor organization, the F.S.B., in the 1990s, according to Andrei Soldatov, a Russian journalist who has just published a study of that organization called "The New Nobility."
One of Mr. Safonov's subsequent assignments in the 2000s was to head a joint British-Russian counterterrorism group, which was dissolved in the diplomatic freeze provoked by Mr. Litvinenko's death, Mr. Soldatov said in a telephone interview.
According to the leaked cable, "Safonov claimed that Russian authorities in London had known about and followed individuals moving radioactive substances into the city, but were told by the British that they were under control before the poisoning took place."
The cable did not identify the people carrying the material. Mr. Safonov's comments reflected allegations by Mr. Lugovoi who, at the time, accused Mr. Litvinenko of being in the pay of British intelligence.
But Mr. Safonov's remarks seemed likely to be taken by British officials as an accusation of incompetence, with the poisoning happening under their eyes. If confirmed, they would also raise the question of how Britain reacted to the idea of Russian spies tailing their citizens on British soil.
The question of who ordered the killing surfaced in a separate leaked cable, also marked "secret," about a meeting in Paris -- on the same day as the former spies' dinner -- between a French presidential adviser, Maurice Gourdault-Montagne and Mr. Fried, then the assistant secretary of state for European and Eurasian affairs in the Bush administration.
Mr. Fried is now the Guantánamo special envoy, appointed by President Obama and charged with persuading other countries to take detainees held at the prison in Cuba.
The French official, the cable said, ascribed the killing to "rogue elements" in the Russian security services. But Mr. Fried "commented that the short-term trend inside Russia was negative, noting increasing indications that the U.K. investigation into the murder of Litvinenko could well point to some sort of Russian involvement."
Later, it said: "Fried, noting Putin's attention to detail, questioned whether rogue security elements could operate, in the U.K. no less, without Putin's knowledge. Describing the current atmosphere as strange, he described the Russians as increasingly self-confident, to the point of arrogance."
Mr. Fried's reported remark was the first time that such a suggestion by a serving American officer was made public.
That remark reflected some suspicions about high-level Kremlin involvement in the period after Mr. Litvinenko's death, when conspiracy theories blossomed relating to Mr. Litvinenko's activities as a visceral public enemy of Mr. Putin and as a whistle-blower on Russian organized crime.
Mr. Litvinenko fled Russia in 2000 and sought asylum in Britain, where he acquired British citizenship shortly before his death.
Mr. Fried declined to comment publicly on the content of the cable.
Another cable, from the American Embassy in Madrid, marked "confidential" and dated Aug. 31, 2009, cited an article in the newspaper El País.
The article said that Mr. Litvinenko had tipped off Spanish security officials about Russian organized crime figures in Spain and had provided information about four suspected gangsters at a previously unrecorded meeting with Spanish officials in May 2006.
That report added one more layer to the debate about the motives of his killers -- could the killing have been done in revenge for his disclosures about the mob?
Perhaps the most tantalizing item in the cables was related to Dmitri Kovtun, a business associate of Mr. Lugovoi, who passed through Hamburg on his way to London on Nov. 1 and was, by his own account, present when Mr. Lugovoi met Mr. Litvinenko at the Millennium Hotel in the Mayfair district of London on Nov. 1, 2006.
According to a confidential cable from the American consulate in Hamburg, dated Dec. 19, 2006 -- about a month after Mr. Litvinenko's death -- a senior German counterterrorism official, Gerhard Schindler, "said Kovtun left polonium traces on everything he touched" in Hamburg. That much had been publicly reported.
But, the cable said, "German investigators concluded Kovtun did not have polonium traces on his skin or clothes; Schindler said the polonium was coming out of his body, for example through his pores."
That suggested that the exposure took place during an earlier visit to London by Mr. Lugovoi and Mr. Kovtun in October 2006, during which they had met Mr. Litvinenko; they claimed later that they themselves had been victims of a poisoning attempt. Mr. Litvinenko's supporters and British investigators, however, have long described the earlier visit as a part of the conspiracy against Mr. Litvinenko.
The cable from Hamburg said no traces of polonium were found on the Germanwings plane Mr. Kovtun took to London, and German authorities had been preparing to ground the Aeroflot plane that took him to Hamburg from Moscow to test it for traces of the isotope.
"Schindler said Russian authorities must have found out about German plans because 'at the last minute' Aeroflot swapped planes," the cable said. "Schindler said he did not expect Aeroflot to fly the other plane to Germany any time soon."