Supporters could say the relatives attempted an immediate elaborate, risky and complex frame to inherit from the deceased. But the relatives didn't need to do this as they were already rich.
So a piece of land is brought up. Which Bamber didn't know he would own. Which Nevill may have been going to sell anyway. No value has ever been given on this land.
The final reason for the relatives successful frame is they thought Bamber was guilty. So framed him !