Circumstances under which and the extent to which the Due Process Clauses, the Compulsory Process Clause, and other federal constitutional guarantees prohibit the exclusion of exculpatory evidence in criminal trials.

Davis v. Washington, 547 U.S. 813, 833 (2006) ("We take no position on the standards necessary to demonstrate such forfeiture [of the Sixth Amendment right of confrontation due to misconduct of the....The government can have the burden of proof on factual issues other than the essential elements of the crime charged and the government's burden of persuasion on such "collateral" issues can be and often is less than proof beyond a reasonable doubt. Conversely, sometimes a criminal defendant rather than the government has the burden of proof and persuasion with respect to factual issues that arise under legal rules and requirements apart from the essential elements of the crime charged; for example, a defendant may have the burden of establishing a defense such as duress.

Fed. R. Evid. 609(b) ("unless the court determines, in the interests of justice, that the probative value of the conviction supported by specific facts and circumstances substantially outweighs its prejudicial effect").Although a conviction is generally inadmissible to impeach a witness if more than ten years have elapsed since the later of (i) the date of a witness's conviction or (ii) the witness's release of from imprisonment for that conviction, a trial court court can admit such an "old" conviction if the trial court finds that admission of the conviction is in the interests of justice and that specific facts and circumstances show that the probative value of the conviction substantially outweighs its prejudicial effect.

United States v. Urqhart, 469 F.3d 745, 748-749 (8th Cir. 2006) (upholding trial court's admission of Quinn's written Certificate of Nonexistence of Record [CNR] which did not violate defendant's rights under....The right of confrontation guaranteed by the Confrontation Clause of the Sixth Amendment to the U.S. Constitution puts no constraints on the admissibility of nontestimonial hearsay statements; the federal constitutional right of confrontation does not apply to such statements.