essentialone:
In court, it's not enough to know a fact - you have to be able to prove it. That means you have to be able to convince a jury or a judge that the fact is most likely true. Proving a fact requires evidence - something reliable to help convince the jury or judge.

But this is not a court. This is we trying to infer, based on this or that.

Infer what exactly?

essentialone:
Is it possible at all for one to be killed diabolically?
Not yet asking for the evidence. Rather asking for the possibility. We come later to evidence.

Recall your very question above.

An inference is made from evidence and reasoning , so where do we begin with the evidence for your OP claim or at least the reasoning behind the claim that your relatives killed your father.