It is quite possible that Russia is killing whistleblowers and critics of Putin. However, proving it is a different matter. You could easily argue that the US, UK, China, country of your choice, is doing the same thing. It is a fine line, although with the state control of media and Putin's censorship of criticism, and the fact that the he appears to be leaning towards Soviet Style controls over the population, I would probably have to say that I am more inclined to believe it is happening, than not