If you want to send a message, you don't make it a plausible accident. And if you really want to send a message loud and clear, you let it be understood that this was no rogue element; the whole government backs this up: another branch of the executive, the judiciary (no review), and the legislative (no investigative committee).

Yeah - completely farcical ruling.

However, surely if he was killed to order, the people responsible would make it far less obvious, and if it was attempted to be covered up - surely it wouldn't be as poorly done as this?

Yes, but exactly the same logic could be applied to Litvinenko. Death by plutonium is so obvious that one might think it was meant to be that way.

I can see the use of killing someone with a painful, elongated death by polonium poisoning, it's obvious, and makes a statement. I don't feel the same can be said for making the body of someone appear in a locked bag though - people's reactions are closer to "WTF?" rather than shock.