In the photo above former Russian security agent Alexander Litvinenko is shown in his London hospital bed just before his death.

Litvinenko was a very vocal and vehement critic of the Putin regime.

On Oct. 19, 2006, at a public meeting in London, he introduced himself as a former Russian KGB officer, and proceeded to accuse President Vladimir Putin of sanctioning the murder two weeks earlier of a crusading Russian journalist, Anna Politkovskaya. Litvinenko fell out with his erstwhile employers after claiming they had ordered him to assassinate Boris Berezovsky, an oligarch and high Russian official of the Yeltsin years, now exiled in London. Litvinenko was employed by billionaire Berezovsky and had met Politkovskaya on several occasions.

Litvinenko died in a London hospital, after having ingested a "major dose" of the radioactive toxin polonium-210 that destroyed his immune system, according to Britain's Health Protection Agency. Scotland Yard said that traces of polonium-210 — which is so rare and volatile that producing quantities large enough to kill requires access to a high-security nuclear laboratory — were found at a sushi restaurant called Itsu in Piccadilly where Litvinenko had eaten lunch on the day he got sick. Traces of the isotope were also found at his north London home and at the Millennium Hotel in Grosvenor Square, which he had also visited.

It is said that only governments have access to material like Polonium-210 because it is produced either in a nuclear reactor or in a particle accelerator. A nuclear reactor used for producing electricity could produce Polonium-210.

Exactly how or why the dose was administered, and by whom, remains a mystery. The Litvinenko case revived memories of perhaps the most notorious assassination carried out during the cold war, the 1978 murder in London of Georgi Markov, a Bulgarian dissident who was working for the BBC. He was killed with a ricin-tipped umbrella while waiting for a bus, in a case that has never been solved. Just as in that Markov case, the death of Litvinenko has already given rise to a flurry of conspiracy theories, including speculation among defenders of Putin's government that the poisoning had been arranged by Russian exiles or by foreign intelligence agencies to discredit Moscow.

After ingesting poison, it took over thee weeks for the ex-spy to die. His death came after a massive heart attack which followed the failure of his vital organs like his liver. So, after taking poison, his body started withering away and slowly disintegrating. He had a really long, and painful death.

His Islamic Funeral

Just before his death, the former spy had expressed his desire to his father that he be buried in a mosque. However, due to health concerns, his coffin was not allowed in the London mosque.

At Highgate Cemetery in north London, Litvinenko’s irradiated body was buried in a lead-lined, air tight coffin. Gathered for the ceremony were some of the key figures hated by Kremlin.

On one side, the British government is angry at what may prove to be a foreign radiological attack in London. On the other, the Kremlin has long been seething with anger that Britain has given refuge to its enemies, such as Berezovsky and Zakayev, whom it wants to extradite for alleged crimes in Russia.

Latest story about why he was killed

An ex-business associate of Alexander Litvinenko said the former Russian spy was murdered because of information he held on a powerful Kremlin figure. Ex-spy Yuri Shvets said Mr Litvinenko was commissioned by a reputable UK firm to provide information on Russia. He told BBC Radio 4 that Mr Litvinenko was poisoned after his dossier containing damaging details was deliberately leaked to the high-ranking Moscow figure. He said the British company wanted the eight-page dossier of commercial and political information before it invested millions of pounds in Russia.

About Polonium

Discovered by Marie Curie in 1898, and named after Poland, her native land, polonium has a silvery appearance and is soluble in liquids. Polonium-210, is its most readily available variant. Other isotopes of the element can decay in milliseconds. Although it is extremely toxic and highly radioactive - just one milligram would emit as much radiation as five grams of radium - the metal emits short-range alpha rays, which would not be picked up by conventional radiation scanners. It was detected only in Alexander Litvinenko's urine.

Polonium-210 is found naturally in the human body, as well as in tobacco and uranium ore, but in minuscule quantities. Although a tiny speck can be fatal, the amount needed to kill would have to be made in a nuclear laboratory. The metal has to be ingested by breathing, eating or drinking, or through an open wound; it cannot be absorbed by skin contact.

Inside the body, radioactive waves pound cells, destroying them outright or causing genetic mutations. As it decays, polonium-210 generates great heat: half a gram creates 140 watts of energy. The metal was used by the Soviet space programme in the 1970s as a portable heat generator for Lunokhod lunar rovers.