How the lethal dose of polonium was discovered

A public inquiry into the death of Alexander Litvinenko is taking place, nearly eight years after he was poisoned.

Our World has been speaking to many of the key players and piecing together the story on how he was murdered.

Here Prof Ian Shipsey, one of the world's leading particle physicists, demonstrates how to test for polonium poisoning.

Litvinenko: A deadly trail of polonium

Find out more and watch more clips at Our World's website.

You can see Our World: A Very Political Assassination on BBC World News on Friday 31 July at 21:30 GMT and on Saturday 1 August at 00:30 and 03:30 GMT. In the UK the programme can be seen on the BBC News Channel on Saturday 1 August at 04:30 and 21:30 BST and on Sunday 2 August at 03:30 BST.