wash

サスペンス小説A Stranger is Watchingを読んでいます。死刑判決により処刑寸前となった死刑囚の弁護士が、殺された妻の夫であり死刑制度の擁護者でもあるPetersonのところに処刑を中止させようと最後の説得をしに来ました。
'If he were a killer would he have left an eyewitness like Neil? Would he have left Mrs Perry alive knowing she probably recognized him? She shops in Timberly's. A killer doesn't leave witnesses, Mr Peterson.'
Hugh shook his head. 'It doesn't wash. It's all conjecture. There isn't a scrap of proof in this.'
HughはPetersonと一緒にいた刑事ですが、そのHughが言った "It doesn't wash" の "wash" は何でしょうか？　早速辞書を見ます。
・Oxford English Dictionary: Seem convincing or genuine:‘charm won’t wash with this crew’
・Vocabulary.com: admit to testing or proof: This silly excuse won't wash in traffic court.
・Dictionary.com: to be found true, valid, or real when tested or closely scrutinized; stand being put to the proof: His honesty won't wash.
どうも普通は否定形で使われ、信用できない、当てにならないという様な意味に なるようだ。