I'm not one for conspiracies

And usually Charles Krauthammer is not either...

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The poisoning of Alexander Litvinenko, renegade Russian spy and fierce critic of Vladimir Putin's government, is everywhere being called a mystery. There is dark speculation about unnamed "rogue elements" either in the Russian secret services or among ultranationalists acting independently of the government. There are whispers about the indeterminacy of things in the shadowy netherworld of Russian exile politics, crime and espionage.
...

Some say that the Litvinenko murder was so obvious, so bold, so messy -- five airplanes contaminated, 30,000 people alerted, dozens of places in London radioactive -- that it could not possibly have been the KGB.

But that's the beauty of it. Do it obvious, do it brazen, and count on those too-clever-by-half Westerners to find that exonerating. ...

The other reason for making it obvious and brazen is to send a message. This is a warning to all the future Litvinenkos of what awaits them if they continue to go after the Russian government. They'll get you even in London, where there is the rule of law. And they'll get you even if it makes negative headlines for a month.
...

But even Litvinenko's personal smallness serves the KGB's purposes precisely. If they go to such lengths and such messiness and such risk to kill someone as small as Litvinenko, then no critic of the Putin dictatorship is safe. It is the ultimate in deterrence.