It's a year since former Russian security officer Alexander Litvinenko died in a London hospital. His death, caused by a rare radioactive substance – Polonium 210 – worsened relations between Britain and Russia. The countries accuse

MI6 agent

“A former KGB spy” – that’s what Aleksandr Litvinenko was called in Britain. But in the latest twist to the story, a British newspaper, the Daily Mail, quotes diplomatic and intelligence sources, claiming that Litvinenko was an MI6 agent. The paper says he was receiving around £2,000 a month from the British security services at the time of his murder.

Isotope mystery

Polonium 210, the highly toxic radioactive substance used to poison Litvinenko, came under close scrutiny after the murder. But experts say the source of the isotope is almost impossible to track down. So did it come from Russia or somewhere else?

“It is the kind of attack that cannot be linked to a government,” says Robert Burns, a military writer for the Associated Press .

“Kennedy’s assassination”

Andrey Lugovoy is the Russian citizen who has been formally accused of the murder by Britain's Crown Prosecution Service. The UK is calling for his extradition. Russia has refused the request, as the country's constitution prohibits the extradition of its citizens. “Where is the proof of Lugovoy's guilt?” ask the Russian authorities.

Britain's response was to expel four Russian diplomats. Days later, Moscow responded with the tit-for-tat expulsion of four British officials.

Lugovoy, who is still in Russia, calls on the British media to look for answers to the questions that remain unclear.

“If the British public disagrees with the position taken by current British leadership and starts asking questions there is a chance the truth will prevail. We offered British journalists our own facts and proof of our innocence. We also hope they will conduct their own investigation. We feel that attitudes in Britain towards this whole story are changing,” Lugovoy says.

“It’s like the Kennedy assassination – there’ll be conspiracy theories for years, decades to come. We know a certain amount but there’s an underlying truth that we’ll just never find out about,” says James Nixey from Chatham House, an NGO dedicated to the analysis of world affairs.

With so many disputed claims a year on there are still more questions than answers in this case. And with the inquest adjourned indefinitely, the public’s interest has definitely moved on.