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, swearing(noun) a commitment to tell the truth (especially in a court of law); to lie under oath is to become subject to prosecution for perjury. oath(noun) a solemn promise, usually invoking a divine witness, regarding your future acts or behavior.