How has the US Federal Bureau of Investigation assessed the credibility of an applicant's testimony at a hearing?

Having questioned Suo's credibility, the agency reasonably relied further on his failure to provide relevant corroborating evidence sufficient to rehabilitate his testimony: Suo did not present any documentary evidence showing that he had been arrested and detained in China, and neither he nor his witnesses presented any documents to show that they had worked together at restaurants in New Hampshire and Massachusetts. "An applicant's failure to corroborate his [] testimony may bear on credibility, because the absence of corroboration in general makes an applicant unable to rehabilitate testimony that has already been called into question." Biao Yang v. Gonzales, 496 F.3d 268, 273 (2d Cir. 2007).