British officials are still puzzled by the use of this poison, the radioactive isotope Polonium 210.
But since access to polonium is limited to state agencies, many suspect FSB involvement.
Mr Litvinenko died in 2006 after he was apparently poisoned with the radioactive substance polonium-210.
BBC: Alexander Litvinenko murder was 'London nuclear terror'
In Britain, 700 people were tested for polonium contamination and 670 were tested abroad including Lugovoi.
Litvinenko, a prominent critic of Russian President Vladimir Putin, is believed to have died from ingesting radioactive polonium-210.
He died at a London hospital November 23, 2006, after being poisoned by the radioactive material polonium-210.
Prosecutor General Yuri Chaika told reporters Tuesday that it's nonsense to assume the rare polonium-210 isotope came from Russia.
Doctors have also found low levels of polonium-210 in Scaramella's system, though he said he did not feel ill.
Lugovoi also said he has evidence of London's involvement in the death of Litvinenko, who was dosed with radioactive polonium-210.
Alexander Litvinenko, a renegade Russian security officer living in London, was killed by poisoning with polonium, a rare radioactive substance, in 2006.
Litvinenko died Nov. 23 in a London hospital after ingesting radioactive polonium-210.
Litvinenko wound up dead in London from poisoning with an exotic, highly radioactive element called Polonium 210 widely believed to have come from Russia.
Traces of polonium-210 were found at around a dozen other sites in London, including three hotels, a stadium, two planes and an office building.
One instrument for doing so is radioactive substance called Polonium 210, stuff so toxic that even the assassins seem to be dying from it.
That is the formula the report applies, for example, to Iran's explanation for having conducted research on polonium-210, which can be useful for triggering nuclear weapons.
On that day Litvinenko fell sick, suffering (it eventually turned out) the effects of poisoning by polonium, a rare radioactive substance that killed him three weeks later.
And Mr. Lugovoi, he gave an interview yesterday actually in Moscow, where he denied involvement again and in fact said he was a victim himself of polonium poisoning.
Russian investigators have appeared recalcitrant in the Livtinenko case, and the government has refused to extradite the polonium suspect, Andrei Lugovoi, calling it a matter of national sovereignty.
He was a friend and close associate of Alexander Litvinenko, the former Russian security agent who died in London in 2006 after drinking tea laced with radioactive polonium.
On Wednesday Russia's Investigative Committee said it had also conducted its own probe, and had ascertained that Mr. Lugovoi and a colleague, Dmitry Kovtun, were also exposed to polonium in the restaurant.
The accused has always maintained his innocence, as have the other Russians, and indeed Mr Lugovoi claims to be a co-victim of the polonium plot rather than the perpetrator of the crime.
Lugovoi, a millionaire with a background in the private security business, had met with Litvinenko in London on Nov. 1, hours before the former KGB operative said he felt ill from poisoning by radioactive substance polonium-210.
Mr Berezovsky was a close friend of murdered Russian emigre and former KGB officer Alexander Litvinenko, who died in 2006 after he was poisoned with the radioactive material polonium-210 while drinking tea at a London meeting.
"We don't have enough information to make any definitive statement, but it does seem a bit of a stretch" to conclude that Arafat was poisoned by polonium-210, he told CNN in a telephone interview last week.
"We have evidence there is too much polonium, but we also have hints from the medical records that this may not be the case, " said Francois Bochud, director of the Institut de Radiophysique in Lausanne, Switzerland.
The Russian government professed co-operation with British police who visited Moscow in the course of their inquiries, but has angrily rejected any suggestion of Kremlin involvement, even denying that the polonium used to kill Litvinenko could have come from Russia.
British police say they have amassed detailed evidence against Mr. Lugovoi, a career security service officer, and tracked a trail of polonium across Europe to his London hotel room and the upscale Mayfair bar where he met with Mr. Litvenenko when he consumed some polonium-laced tea.
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