The reasonable doubt that requires an acquittal is a reasonable doubt rather than a merely possible, speculative, conjectural, or fanciful doubt.

Fed. R. Evid. 703 advisory committee's note ("Facts or data upon which expert opinions are based may, under the rule, be derived from three possible sources. ... The third source contemplated by the rule consists of presentation of data to the expert outside of court and other than by his own perception. In this respect the rule is...An expert witness may base his or her opinion on hearsay evidence if the hearsay evidence relied on by the witness is the type of hearsay customarily and reasonably relied on by experts in the witness's field.

Buckley v. Mukasey, 538 F.3d 306, 319 (4th Cir. 2008) (vacating judgment and remanding for further proceedings in a retaliation claim in which the trial court excluded Segar litigation evidence, on ground that plaintiff "intended to utilize the Segar litigation evidence to demonstrate retaliatory animus,...A person's other crimes, wrongs, or acts are not barred by the character rule either if they are not offered to show that person's propensity or if they are not offered to show that that person engaged in conduct on a particular occasion because of his or her propensity to engage in that sort of conduct.

See United States v. Trala, 386 F.3d 536, 545 (3d Cir. 2004) (upholding trial court's admission of the conflicting statements of defendant's girlfriend to a police officer because "[defendant's] rights under the....If a declarant is unavailable to testify at the time of trial, a criminal defendant's federal constitutional right to confront, cross-examine, and impeach an adverse witness is satisfied if the defendant had an adequate opportunity in a prior proceeding to confront, cross-examine, and impeach the unavailable declarant.