In an exclusive interview, senior Russian policeman Lieutenant-Colonel Oleg Silchenko denies inflicting suffering amounting to torture on the jailed Russian lawyer Sergei Magnitsky, and hits back at his accusers. Silchenko - now at the the centre of a growing international row over the mysterious death of the prominent whistleblower - is high on a list of Russian officials now facing possible sanctions by the United States, as Tim Whewell reports. Presented by Jeremy Paxman.