United States v. McGowan, 668 F.3d 601 (9th Cir. Jan. 26, 2012) (federal sentencing court violated due process, by relying on unreliable, unsubstantiated allegations in imposing sentence, where prisoner witness made unreliable allegations that defendant prison guard smuggled drugs into prison; there was no further evidence in record or inference that might be drawn in support of prisoner's extremely serious charges, there was no explanation as to why defendant would have engaged in such felonious conduct with prisoner, and sentencing judge had no opportunity to observe prisoner in order to evaluate his credibility).