However, both of these incidents are just a few miles from a Brit chemical weapons facility.
Which is more likely:
1. The Russians brought more than needed when they came to kill an ex spy and left it in a dumpster where a couple of addicts found months later.
2. The Russians returned for a random killing.
3. Theresa May's feckless government killed the ex spies either as a false flag, or because they were suspected double agents and security at the weapons facility isn't any more competent than the rest of what passes for government in old blighty.
I initially assumed option one, now I lean towards the third possibility.
Your post offers sound possibilities to consider. I would add another. What if there is a crazy, or malicious, employee at Porton Down, who is doing this?