"This is hours old and the full facts are still to be ascertained as those involved are debriefed," officials said.
early 15c., "to inform, to give assurance," from Anglo-French acerteiner, Old French acertener "to assure, certify" (13c.), from a "to" (see ad-) + certain "certain" (see certain). Modern meaning of "find out for sure by experiment or investigation" is first attested 1794. Related: Ascertained; ascertaining.