You're not gonna go anywhere with him Theo, there is always a goal post to move or some other "plausible" explanation that will suddenly pop up when the need arises.
I did much the same in the Skrypal thread with many others, it's futile. it went from "we don't know" to "maybe it's england" to "definitely not Russia" to "food poisoning " to "maybe they tripped and fell on it" and then back to "Novichok compound was not even pure so it's BS" again.
Same for all the other dissenters and political opponents. they all just happen to run in some polonium tea by accident or just happen to get randomly gunned down by "completely random" thugs
hell even in this thread his main goal is asking you to prove Porton Down does anal probes.....