The "reliable source" here is the German Government. It has confirmed that, yes, Navalny was poisoned, and yes, he was poisoned with a hard to obtain poison tha

The "reliable source" here is the German Government. It has confirmed that, yes, Navalny was poisoned, and yes, he was poisoned with a hard to obtain poison that has been used in the past by the Russian government. This does seem to reduce the likelihood that Navalny wasn't poisoned, or that he was poisoned by someone unconnected to the government. MattGaiser's argument is that the implied threat is the goal, which is helped by confirmation of the above.