Five weeks after Alexander Litvinenko suddenly fell ill at the hands of an unknown poisoner, the riddle of his murder and the uneasy diplomatic stand-off that surrounds it grew ever more knotted in intrigue and tragedy.
As the former Russian spy's radioactive body was laid to rest in a north London cemetery, the authorities in Moscow announced they were investigating the attempted murder of one of his business associates.
Dmitry Kovtun, one of two Russian businessmen who met Mr Litvinenko on several occasions in London prior to his assassination, was reported to be in a coma in a Moscow hospital last night after testing positive for polonium-210.
In a day of further twists, it was revealed that seven workers at the Millennium Hotel in Mayfair, where the men met on 1 November, had also tested positive for the radioactive isotope.
The discovery of significant levels of contamination last night moved the hotel centre stage in the effort to pinpoint where and when Mr Litvinenko and Mr Kovtun were contaminated.
The Interfax news agency said it had been told by unnamed sources that doctors treating Mr Kovtun, 40, were describing his condition as "critical".
But the claim was strongly contested by his lawyers, who said he was still conscious after twice being questioned by Russian investigators and Scotland Yard detectives since Tuesday. The Independent was told by sources close to Mr Kovtun that he was talking and sitting up in bed.
The development came just hours after the office of the Russian prosecutor general said it had launched a criminal investigation into the suspected poisoning of Mr Kovtun, a partner in a Moscow-based security company, and the murder of Mr Litvinenko.
That would allow suspects for the killing of the former KGB agent to be prosecuted in Russia and comes amid increasing manoeuvring over which country has jurisdiction over the case.
On Tuesday, the prosecutor general, Yuri Chaika, banned British detectives from questioning interviewees and ruled out any extradition of Russian citizens to face a trial.
Investigators in Moscow last night raised the possibility of sending Russian police to London to pursue their own inquiry.
A spokesman said: "The necessity of a visit by Russian investigators to London may arise, and we hope for the understanding and help of the British side."
Scotland Yard appeared to distance itself from the investigation into Mr Kovtun despite Russian insistence that he had been poisoned in London. Police sources said that the Russian announcement "had little impact" on its investigation in Mr Litvinenko's murder.
But in a statement, Mr Chaika's office said last night: "We have opened a criminal case in connection with the murder of Alexander Litvinenko and the attempted murder of Dmitry Kovtun.
"As a result of examinations, it was established Mr Litvinenko died as a result of poisoning by a radioactive substance and Mr Kovtun, who met Mr Litvinenko in London in October 2006, developed an illness also connected with the substance."
The sudden deterioration in Mr Kovtun's condition represented a dramatic turn in the saga. From the use of quantities of polonium-210, believed to have cost millions, to the contamination of BA aircraft, the death of Mr Litvinenko has provoked claims it could only have taken place with state involvement. The Kremlin has dismissed such allegations as "sheer nonsense".
Mr Kovtun's illness had previously not been made public and he had been privately regarded as a witness or even a suspect, rather than a victim.
The businessman met Mr Litvinenko at the Millennium Hotel in Mayfair on 1 November - the date on which the former KGB man was widely believed to have fallen ill.
Traces of polonium-210, which was found in Mr Litvinenko's body, have been found in Mr Kovtun's digestive tract, suggesting he too had eaten or drunk something laced with the poison.
In a separate move, the Health Protection Agency said seven staff at the Pine Bar in the hotel where the men met had tested positive for low levels of the substance. The HPA said: "There is no health risk in the short-term and in the long-term the risk is judged to be very small."
It is already known that Mr Litvinenko's widow, Marina, suffered low-level contamination. But Dr Michael Clark, head of the HPA's radiation protection division, raised the prospect that other family members - Mr Litvinenko's father, Walter, and 12-year-old son, Anatole - had also tested positive.
Dr Clark said: "The levels of radiation found among hotel staff are less than the family member we identified but they are approaching it."
It is understood that detectives are also exploring whether Mr Litvinenko, 43, who died on 23 November, and Mr Kovtun were attacked before their 1 November meeting and may have been spreading contamination for a number of days.
Mr Kovtun is known to have spent three days in London from 16 October during which time he shared two meals with Mr Litvinenko, who had become a "fixer" for his trips to London. One of the meals was in the same Itsu sushi bar on Piccadilly where Mr Litvinenko ate on 1 November with another man, the Italian security expert Mario Scaramella.
A notable omission from the Russian investigator's statement was the name of Andrei Lugovoy, a former KGB bodyguard, who was last night also being tested for polonium-210 poisoning at an unnamed Moscow clinic. A meeting between detectives from the Yard's anti-terrorist command and Mr Lugovoi was yesterday postponed for the third time in as many days.
Curiouser and curiouser: the story that becomes more mysterious by the day
Litvinenko meets former KGB bodyguard Andrei Lugovoy and an associate, Dmitry Kovtun at the Millennium Hotel in Mayfair, on the same day as meeting Italian academic Mario Scaramella at sushi bar Itsu. Later, he complains of feeling ill and is admitted to Barnet General Hospital
The former spy is moved to intensive care at University College Hospital as Scotland Yard investigate
Litvinenko dies. It is confirmed the next day he had massive amounts of polonium-210 in his body
Radioactive traces are found at the hotel and restaurant visited by Litvinenko. His family issues a statement he compiled while in hospital in which he exhorts President Vladimir Putin: "May God forgive you for what you have done". The Kremlin dismissed allegations it was involved
NHS Direct say hundreds of people have called, worried about poisoning
Mr Scaramella arrives in Britain to be interviewed as a potential witness. Home Secretary John Reid confirms the Foreign Office has told Russian authorities they were expected to "offer all necessary co-operation"
Polonium-210 found at the Mayfair office of exiled Russian billionaire Boris Berezovsky
Traces of polonium-210 have been found in 12 places, including on two BA planes at Heathrow
Nine British detective travel to Moscow as part of the investigation
Mr Scaramella tests positive for polonium-210. He is admitted to hospital but does not show symptoms of poisoning. Litvinenko's wife also tests positive for tiny amounts
Scotland Yard say they are now treating Litvinenko's death as murder. Radiation is found at the British embassy in Moscow. Mr Scaramella is discharged from hospital
Litvenko's funeral is held as tests of all seven staff working at the Millenium hotel on 1 November come back with positive traces of low levels of radiation. Russia opens an official inquiry into his murder as well as the attempted murder of Mr Kovtun, the associate he met on 1 November.
The men at The Millennium Hotel
Mr Litvinenko met two Russian business associates, Dmitry Kovtun and Andrei Lugovoy, in the Pine Bar of this Grosvenor Square hotel shortly after 4pm on 1 November. The men said they had flown to London to watch a football match. Mr Litvinenko telephoned at 6.30am the next day to cancel a further meeting, saying he had fallen ill. A third man, named only as Vladimir, later denied he was at the meeting.
The sushi dining partner
Mario Scaramella, an Italian academic and self-styled security expert, met Mr Litvinenko at the Piccadilly branch of the Itsu sushi chain at 3pm on 1 November to discuss what he said was a mutual death threat. The ex-KGB man laughed off the threat. Mr Scaramella later tested positive for traces of polonium-210.
The funeral cortege
Gathered around Mr Litvinenko's graveside yesterday were members of a close circle of prominent Russian exiles. They included Boris Berezovsky, the billionaire oligarch and arch Kremlin opponent; Akhmed Zakayev, the foreign minister of the Chechen government in exile, who was a close neighbour; and Alex Goldfarb, a Washington-based human rights worker, who has become the public face of the family - Mr Litvinenko's widow, Marina, his father, Walter, and his son, Anatole.
The Russian links
As the Scotland Yard investigation headed to Moscow, Yuri Chaika, Russia's chief prosecutor, said that interviews would be conducted by Russian officers and ruled out the extradition of any Russian suspects. Foreign Minister Sergey Lavrov claimed the saga had strained relations with London - he retracted this yesterday.Reuse content