The corroboration that apparently led him to put faith in Ben-Menashe's testimony was retroactive.
corroboration is not needed in a speech intended narrowly for the pre-convinced.
Ruth, in his defense, said that he had been having dinner with friends at the time, and produced two witnesses in corroboration.
mid-15c., "strengthening, support," from Late Latin corroborationem (nominative corroboratio), noun of action from past participle stem of Latin corroborare "to strengthen" (see corroborate). Meaning "confirmation" attested by 1768.