I think the answer to motive is in Wratten’s character. I don’t know if it’s in the documentary but I remember the Paxman interview. Paxman pointed out the “no doubt whatsoever” requirement and Wratten replied,” Well, I am in no doubt whatsoever” . And to him, that was that.
I too was accused of gross negligence under his regime, but I was alive to fight it and “clear my name”