This entertaining speculation might be considered as a reasonable possibility if not for the fact that one would have to accept that Putin's enemies, both domestically and in the CIA had obviously been busy killing and jailing so many of his political challengers all over the world. As a consequence, it cannot be allowed to pass without comment.
There seems to be precedent for the example of Boris Nemtsov in the case of Alexander Litvinenko, an ex-FSB officer (Federal Security Service) who was in exile in London when he was injected with a small capsule containing radioactive polonium. It killed him.
Then there is the similar account of Boris Berezovsky, a Russian media maganate who fled to England to escape prosecution and was then found dead in his Berkshire bathroom. It cannot have been very reassuring for Vladimir Gusinski, the owner of media giant, NTV and Putin critic who was charged with fraud and then fled into exile.
The billionaire head of the Russian oil company, Yukos, Mikhail Khodorkovsky, was charged with fraud and tax evasion, and is imprisoned in Russia, as is Platon Lebdev. Both have been designated by Amnesty International to be prisoners of conscience.
With fraud being the charge of choice to apply to Putin's critics, Alexei Nalvany has found himself to be imprisoned on that very charge.
For a touch of variety, two members of the rock band, p*ssy Riot , who coincidentally had a couple of less than flattering things to say about Vladimir Putin, were imprisoned for a term of two years on charges of hooliganism. Then there is Sergei Udaltsov, the leader of a protest movement who has been under house arrest since 2013 after being charged with incitement to mass disorder.
Journalist Ksenia Sobchak, the daughter of a well connected member of Putin's circle of support was a profile personality on Russian TV until some criticism escaped from her on air. Her career has been derailed, and she has been able to find work only with a television network that seems to occupy a dial position so that it can be ignored.
Still in all, she can count herself as fortunate that she has not yet met the fate of murdered Novaya Gazeta journalist, Anna Politkovskaya, who is one of five Novaya Gazeta journalists to have been murdered or found dead in suspicious circumstances since 2000.Now, I don't for a moment mean to suggest that the CIA is above suspicion when unexpected corpses turn up. After all, there is still the case of American journalist, Michael Hastings that is begging for resolution with a believable explanation. But when looking around for the cause of all of these Putin critics coming to such bad ends, it isn't the CIA or Putin's other critics who spring to mind. With the examples above, my speculation is that Mr. Putin does not need the assistance that may have been offered by the CIA and his as yet unfettered and ambulatory political enemies. And I understand why Mr. Roberts might have been uninterested in receiving commentary on his allegations.