I have already answered this but you keep ignoring it. The vet offered to have him rehomed but Bamber told his to just kill him - what was he supposed to do? Allow the vet to at least try and rehome him.
I haven't ignored what you've said Caroline I just disagree.
It is well documented JB disliked Crispy pre murders.
He understood Crispy's temperament seeing him every working day at the farm and may well have appreciated he wasn't the sort of dog that could be rehomed. Whatever his reason(s) or even an absence of reason it was his choice and decision.
He did not subject Crispy to any cruelty, pain or suffering. Nor did he end his life inhumanely; he went to the time, trouble and expense of having him put down at the vets where JM accompanied him.
The relatives were all farmers with their own farms and none of them came forward to offer Crispy a new home. No one, except those here, has ever criticised JB for having Crispy put down which is a life choice and perfectly legal like a woman's choice to terminate a foetus.