There's no doubt now that the murder of Alexander Litvinenko was sanctioned at the highest level of the Russian mafia state. I think Putin himself was involved either by silent approval or by direct order.
http://www.bbc.co.uk/news/uk-30929940
http://www.bbc.co.uk/news/uk-33734525
http://www.bbc.co.uk/news/uk-30929940
http://www.bbc.co.uk/news/uk-33734525