The men -- Andrei Lugovoi, Dmitry Kovtun, and Vyacheslav Sokolenko -- met with Litvinenko in a London hotel on November 1, the day he fell ill. All three have protested their innocence, and say they are being framed.
British Home Secretary John Reid, speaking ahead of an EU interior ministers meeting in Brussels, says he is confident of Moscow's assistance in the case.
Chechen separatist envoy Akhmed Zakayev told RFE/RL that Litvinenko asked him about the possibility of converting to Islam in the early days of his illness.
MORE: Coverage in Russian from RFE/RL's Russian Service.
"The British police will be going to Russia to continue their inquiries and will continue to go wherever the evidence leads," said Reid. "This investigation will proceed as normal, whatever the diplomatic or whatever the wider considerations."
Newspaper reports say a separate contingent of Scotland Yard investigators was in the United States last week to question a former KGB agent with ties to both Litvinenko and Litvinenko's London ally, exiled Russian billionaire Boris Berezovsky.
The man, Yury Shvets, told the Associated Press he had given the British officers the name of the person he believes is behind Litvinenko's death. He declined to elaborate.
The widening investigation follows revelations last week that radioactive traces had been found on airplanes that traveled between London and Moscow, as well as to a dozen other European cities during the month of November.
A fourth man who met Litvinenko on the day of his apparent poisoning has also been found to have ingested a significant amount of polonium-210.
Mario Scaramella, an Italian academic and security consultant, is currently in London's University College Hospital. He claims to have "five times" the deadly dose of the radioactive substance in his body, although doctors say he remains well.
British officials have raced to counter growing public fear as traces of radioactivity have been detected in a dozen London locations and on board aircraft.
Home Secretary Reid today tried to assuage EU concerns about public safety, saying, "I'm very glad to have the opportunity to be here to inform my European colleagues of developments on the case of Mr. Litvinenko and hopefully to reassure them as well so that they're aware that any health threat is absolutely minimal."
No Easy Answers
Investigators appear no closer to resolving the Litvinenko case. In the absence of a clear resolution, multiple theories have developed to explain what may be behind the mysterious death of the former security-service agent.
Litvinenko's friends and family say his death was a vendetta carried out by the Kremlin.
The 43-year-old Litvinenko had lived in England since 2000, and was a fierce critic of the Russian government. He had accused the Kremlin of involvement in a number of terrorist-style bombings, assassinations, and murder attempts.
Litvinenko wrote a deathbed letter claiming his poisoning was the work of Russian President Vladimir Putin, whom he described as "barbaric and ruthless."
Putin has reportedly criticized the British government for allowing the contents of the letter to be made public. He has denied any Kremlin involvement in Litvinenko's death, saying the plot is the work of anti-Russian forces in the West.
Russian officials have also criticized British authorities for refusing to reveal the results of Litvinenko's autopsy, conducted on December 1. The findings are expected this week.
The date of Litvinenko's funeral has also not been disclosed. Friends say the casket will be sealed to prevent the spread of radiation.
Litvinenko's father today told RFE/RL's Russian Service that his son told him shortly before his death that had converted to Islam, and wished to be buried according to Muslim tradition.
"He told me about his decision two days before he died. He said, 'Papa, I have to talk to you about something serious. I've become a Muslim,'" Valter Litvinenko said.
"I said, 'Sasha, it's your decision. As long as you don't become a communist or a satanist, that's the main thing. I'm a Christian myself, but I have a granddaughter whose father is Kabardin -- my daughter's husband, he's Muslim as well," he continued. "We haven't lost God; we believe in God. But how to believe in God, how to pray -- everyone should do that in the way they consider best."
Valter Litvinenko said his son had grown disenchanted with what he described as the "hierarchy" of the Russian Orthodox Church, and had sought a change.
Akhmed Zakayev, the London-exiled Chechen separatist envoy, told RFE/RL that Litvinenko asked him about the possibility of converting in the early days of his illness. "I told him it was a purely personal question, that it isn't important to which god we pray as long as we aren't doing ignoble acts. And I sort of dropped it. But he over and over again returned to the subject."
Zakayev added that Litvinenko went on to pronounce the shahadah, the fundamental Muslim statement of faith.
"Any student of Islam will tell you that there are no particular rituals for converting to Islam. All you have to do is say one sura" -- a verse or chapter from the Koran -- "and from that moment if the person who pronounces this sura, this shahadah, has sincere intentions, from that moment he is considered a Muslim," he said.
Zakayev also described the day before Litvinenko died: "On November 22, at his request, I, with his wife's approval, brought an imam to him. He read over him a sura from the Koran, the one that is read over a dying Muslim," he said. "Of course, according to Muslim rituals, they pray over the body before burial. Now, unfortunately, that part of the process which Aleksandr requested cannot be fulfilled because of the exceptional circumstances of the radiation in his body and the fact that the coffin that will contain his body cannot be opened for 6 1/2 years."
(with agency reports)
- Polonium, also called "radium F," was discovered by Marie Curie and her husband, Pierre Curie, in 1898 and was later named after Marie's homeland of Poland (Latin: Polonia).
- It is an alpha emitter, meaning that although it is highly radioactive, it cannot penetrate human skin or a sheet of paper. Washing eliminates traces.
- Contact with a carrier's sweat or urine could lead to exposure. But polonium-210 must be ingested or inhaled to cause damage.
- Polonium-210 has a relatively short half-life of 138 days.
- Polonium-210 occurs naturally in the environment (it is found in such things as dirt and tobacco) and in people at low concentrations. But acquiring a lethal amount would require individuals with expertise and connections.
- Polonium-210 emits 5,000 times more alpha particles than radium, and an amount the size of the period at the end of this sentence would contain about 3,400 times the lethal dose. A dose like the one that killed former Russian spy Aleksandr Litvinenko would probably have been manufactured at a nuclear facility.
- Russia exports 8 grams of polonium-210 monthly, all of it to the United States. Exports to Britain ended about five years ago.