Alexander Litvinenko was a former colonel in the Russian secret service, but fled to London seeking political asylum when he became critical of the Putin government in 2000. In November 2006 he was poisoned with the highly radioactive substance Polonium 210. Rebecca Kesby has been speaking to his wife, Marina, about his life and excruciating death.

(PHOTO: Alexander Litvinenko in a London hospital a couple of days before his death in November 2006. Credit Getty Images.)