Has Sugimoto really never mentioned to Asirpa that Wilk denied killing the other Ainu? I know that Sugimoto doesn't like or trust Wilk, or at least his goal of pushing Asirpa to lead the Ainu to independence, so maybe he's afraid telling that to her will encourage her to seek the truth of what happened...but they're already looking for the gold anyway, so it's not that big of a difference. It may also be that he doesn't trust Wilk, and so he doesn't want to get Asirpa's hopes up only for them to get dashed.