And, as far as this case is concerned, what specific evidence would you consider to be "conclusive"?
Ignoring all together my extensive answer to your question and simply repeating your first question?
That's the game you want to play?
Ok, the evidence is conclusive when it is presented, free from assumptions and speculations, in such a way that no reasonable other alternative conclusion can be reached on the basis of that evidence.
Or, as the Oxford Dictionary of Law Enforcement states;
Evidence that must, as a matter of law, be taken to establish some fact in issue and that cannot be disputed.Now let me ask you a question... Would you like to be a defendant in a criminal case where evidence, that can be explained in more ways than one, is used against you on the basis of assumptions and speculations?