Admissibility of scientific and expert evidence depends on a combination of the general scientific or expert acceptance test and a reliability test.

Davis v. Alaska, 415 U.S. 308, pin? (1974).Although the Sixth Amendment right of confrontation is a constraint on the admissibility of inculpatory evidence against a defendant at a criminal trial, the Confrontation Right also guarantees a criminal defendant some means for confronting, challenging, and cross-examining witnesses who testify against him and her. The Sixth Amendment's Confrontation Clause confers on a criminal defendant the right to elicit from an important adverse witness facts -- particularly facts that suggest bias and interest -- that are likely to be significantly probative of the credibility of the testimony of the adverse witness about material facts in issue.

United States v. Mitchell, 145 F.3d 572, 576 (3d Cir. 1998) (vacating judgment of conviction for conspiracy to commit and commission of Hobbs Act robbery, and use of and carrying a firearm during a crime of violence....A statement falls within the hearsay exception provided by Federal Rule of Evidence 803(2) only if the statement is related to a startling event or condition.

United States v. Shryock, 342 F.3d 948, 982 (9th Cir. 2003) (upholding trial court's exclusion of Hernandez's statement under the residual hearsay exception because it did not meet the requirements of Rule 807 as "the....A statement not specifically covered by Federal Rule of Evidence 803 or 804 or by comparable State rules, but having equivalent circumstantial guarantees of trustworthiness, is not excluded by the hearsay rule, if the court determines that (A) the statement is offered as evidence of a material fact; (B) the statement is more probative on the point for which it is offered than any other evidence which the proponent can procure through reasonable efforts; and (C) the general purposes of these rules and the interests of justice will best be served by admission of the statement into evidence.