To answer the original question in my view is that they can't know the truth because the dead no longer are an entity and therefore know nothing, feel nothing and no longer exist. Truth is what living beings believe to be the honest opinion of living and walking beings not some other worldly "all knowing" existence. Hence truth in times of the past was the earth is flat, today earth is round, Both are true relevant to their belief by living human beings at the time. Truth is what is held in the brain until it is changed and a new truth emerges to replace an existing truth.
