A Putin documentary was recently released http://www.bbc.com/news/world-europe-43365800

It was presumably recorded just before the spy was poisoned.

In the documentary, Putin says he can forgive most things, but never forgive betrayal. He talks about it in a context of his cabinet, but he is also an ex-KGB agent and he was similiarly against Snowden (although he gave sanctuary for geopolitical purposes).

It is quite plausible that the 'we will get you if you betray us' is a message to Russians who might have wavering loyalties.

Well it's not like he was hiding. His daughter was working in Moscow and visiting him often. He served his time in Russian jail. It's different for example from Mossad that was killing the terrorists from the Munich Olympics massacre. This was "we find you anywhere" thing.