I admit I've not followed this closely but I've just read an article and bleeding hell this is all just like a proper spy novel.
In the mix are a beautiful femme fatale Russian spy working in America, his spy network transmitted their information as they walked past a reciever disguised as a rock in a Russian park.
His wife and then his son both died within 5 years in questionable circumstances with causes of death being disputed. Some of the Russian agents he exposed working in Britain and America were arrested but others just 'disappeared' without trace.
Now we have this 'unidentified' nerve agent being used in sleepy Wiltshire taking out him and the last of his family.
If you ask me, I doubt this was a command coming from the Kremlin heirarchy or that Putin knew or had anything to do with it.
It smells to me like a rogue attack by one or more very unhappy ex spies who still have 'connections' - who likely suffered greatly on a personal level from his treachery and at some stage swore to exact a dreadful revenge on the bloke and his family - maybe because his actions destroyed their families.