The post mortem into Mr Litvinenko's death opened today in London.Anti-terrorist detectives are following a radioactive trail that they hope will lead them to the former Russian agent's assassins.
What the killers may not have reckoned with is that the polonium 210 that killed Mr Litvinenko, believed to be the only man ever killed with a nuclear poison, left a powerful radioactive "scent" as it was brought to London and inflicted on him.
Developments in the fast-moving tale, which has echoes of a spy thriller, include the revelations that:
• The assassins were so bungling that they dropped the polonium on the floor of a London hotel room, a senior government source told The Daily Telegraph yesterday.
• Scientists at the Atomic Weapons Establishment at Aldermaston are believed to have already identified the nuclear plant which made the polonium.
• Anti-terrorist officers at Scotland Yard believe the polonium was brought into London on a British Airways flight from Moscow on Oct 25, a week before Mr Litvinenko fell ill.
• The Home Secretary told the House of Commons that 12 sites had shown traces of radioactivity and four aircraft were being searched by scientists with sophisticated tracing equipment.
• Aides to Yegor Gaidar, a former prime minister of Russia who fell ill in Ireland last week, claimed he too had been poisoned.
• And detectives are investigating letters smuggled out of Russia which purport to show the existence of a secret squad set up to target Mr Litvinenko and others. Scotland Yard has been passed copies of two letters apparently written in jail by former Russian spy Mikhail Trepashkin, one of which warns Mr Litvinenko that both he and his family are at risk.
The trail of the alpha-radiation was so strong that detectives have been able to follow it across London.
The trail
The senior government source, who is aware of the discussions of the CabinetÂ’s emergency committee, Cobra, said the picture of the killers that was emerging was closer to bungling assassins than cool James Bond-type killers.
Clear traces of the radiation were found on the floor of a room, thought to be in the Millennium hotel in central London, the source said, as well as on a light switch in the same room. The traces were so strong that they indicated the actual source of the radiation was present, not a secondary source such as excretions from Mr LitvinenkoÂ’s contaminated body.
Friends of Mr Litvinenko say that he did not visit the rooms in either of the hotels.
The potential political fall-out from the affair grew as it emerged that the Atomic Weapons Establishment can identify the plant at which the radioactive element was made and are in fact thought to have done so. If that is, as many suspect, in Russia, it could cause acute embarrassment to President Vladimir PutinÂ’s government because its head of nuclear security said recently that no similar material had gone missing in the country.
So new is this type of killing that the murderers may not have known how clearly their weapon of choice would show up, like a glowing trail of footprints around London, followed by Aldermaston scientists with machines called scintillation detectors.
John Reid, the Home Secretary, told the Commons yesterday that traces of radiation had been found at 12 out of 24 sites inspected by experts and that a fourth aircraft was being studied in addition to the three BA flights already grounded and searched. One of those planes, BA Flight 875 from Moscow on Oct 25, is believed to have carried the polonium to London, with traces found on seats and overhead luggage space in both economy and business class.
Last night British Airways announced that one of its three Boeing 767s removed from service following the discovery of low traces of a radioactive substance was given the all-clear by UK government agencies.
Mr Reid said a further Russian plane was "of interest" to police and radiation experts. The studies were all related to the death from radiation poisoning of Mr Litvinenko, the former Russian intelligence officer, in a London hospital last week.
By last night about 5,500 of the 33,000 people who had flown in the affected planes on 221 flights between Oct 25 and Nov 29 had contacted BA. It was later confirmed that Tessa Jowell, the Culture Secretary, and Lord Coe were on the cleared jet.
Mr Reid confirmed that the risk to air passengers was "very low indeed", but said the Government was exercising great caution.
He said that of the 1,700 people who had called to express concern about contamination by 11pm last night, none had so far tested positive for signs of radioactivity.