I see the smoke but not the fire.
GEP, without dragging it all up again, please explain how you KNOW that the pilot concerned was unfit.
I doubt that any of us care how you came to your conclusions, but was there ever any EVIDENCE?
I'm wondering if that's why the CAA were reluctant / unable to act.
If I tell you that I have failed my medical, will that make me a danger to others? I can accept that if I have indeed failed, then I should not be flying, but if my GP is happy, and I'm happy, then wtf has it to do with you?
By all means you are entitled to tell the CAA that you have heard something and seen something that is not a good fit with what you have heard. You should not, however, spread as fact, what you have been told.
How many people (falsely) claim to have lost their medical as a reason for selling an aircraft or share? I suspect that's like selling a bad car on the pretence of moving abroad so you can't take it with you, hence the need for a quick sale.