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
An oath of office is an oath or affirmation a person takes before undertaking the duties of an office, usually a position in government or within a religious body, although such oaths are sometimes required of officers of other organizations.n an inauguration ceremony a new Spanish Prime Minister takes an oath or affirmation of office over an open Constitution, which may be next to a cross and a Bible, and before the King of Spain and other dignitaries.