According to the current principles, as long as there's no proof that something happened otherwise, it is considered to be the truth ... while proof has nothing to do with truth. The proof that 'proves' the official story to be 'true' is proof, and the proof that if found, would prove the official story to be false. Both are proofs. Again, proof has no correlation with truth.
Proof is a thing or an information source which supports one's theories. This is all it does. Supports my theory or proves my theory to be false. Even opposite things can be proven with the right 'proof' and a right interpretation.
If i'm famous for spreading a world view and i suddenly find something that i know with my intellectuelle that if i actually "found" this and published this, it would tear my theories apart and my credibility would be suddenly none existent. So i'd either destroy this evidence that would prove that i was wrong, or i'd hide it, or i'd publish the truth anyway.
A man who has to feed his children, wouldn't consider the last option.