Alexei Navalny: 'Putin is the Tsar of corruption'
23 January 2016 Last updated at 00:30 GMT
The state-sponsored assassination of Alexander Litvinenko raises questions about law and order in Russia.
One man who is an expert on this subject is Russian opposition activist and blogger Alexei Navalny, who has several short spells in prison under his belt.
His brother, Oleg, is in jail now, on, critics say, trumped-up charges as a political hostage.
Mr Navalny has spoken to BBC Newsnight's John Sweeney about Litvinenko, his own fight to free Russia from corruption, and whether it is worth the risk.