This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong; it cannot perjure itself; it cannot be wholly absent. Only its interpretation can err.
Oath definition, a solemn appeal to a deity, or to some revered person or thing, to witness one's determination to speak the truth, to keep a promise, etc.: to testify upon oath. See more. Dictionary.com
oath(Noun) the affirmed statement or promise accepted as equivalent to an oath. oath(Noun) A light or insulting use of a solemn pledge or promise to a god, king or another person, to attest to the truth of a statement or contract the name of a deity in a profanity, as in swearing oaths.