Current scholarship focuses on the prohibition of torture1 and the inadmissibility of confessions or statements obtained through torture.2 The scholarship correctly concludes that involuntary confessions or statements should not be admissible in criminal proceedings. However, little attention has been given to the procedural law governing the standards that judges sitting on international tribunals do or should apply to determine whether a statement or confession was obtained improperly. For example, if a defendant claims that officials obtained his statement through coercive or improper means, what procedures do international tribunals require before deciding whether the statement is admissible into evidence? International and human rights treaties uniformly prohibit the admission of evidence obtained through a violation of human rights. These treaties are ambiguous, however, regarding the standards judges should use to evaluate the credibility of an allegation of impropriety in acquiring a statement or confession. In light of these ambiguities, it is informative and necessary to examine national practices of judicial evaluation of challenged testimonial evidence.
At least in theory, all countries agree that "involuntary confessions must be excluded. Beyond that . . . the rationales and the rigor of exclusionary practices vary greatly."3 Some countries establish mandatory rules that govern judicial assessment of the admissibility of statements. The common law in England requires that a statement or confession be voluntarily given in order to be admissible in court; the common law's insistence on the exclusion of involuntarily confessions is based in part on the refusal to accept oppression or inducement. In the US, a party challenging the legality of a statement or confession may file a motion to suppress; the judge will then hold an evidentiary hearing to assess witness credibility and to determine whether the statement was given knowingly and voluntarily, as is legally required.5 When a defendant alleges that his confession was coerced, however, an automatic rule of exclusion applies and the statement does not come into the trial as evidence.6
Other countries apply more discretionary standards. France applies a relaxed and much less stringent standard that results in the admissibility of most statements if the judge finds that the statement did not substantially violate the rules of criminal procedure.7 The German Code of Criminal Procedure tracks the general trend toward a more discretionary standard, although it does require the mandatory exclusion of statements elicited by certain forbidden means.8 Although these and other states vary in their evaluative standards of such statements, the practice of excluding involuntary or coerced statements qualifies as customary international law. There is broad and established state practice of this specific behavior of excluding certain types of statements. While some states may exclude these statements out of a moral obligation - the desire not to reward coercion or inhuman interrogation practices, for example - such exclusion has also developed into opinio juris. That is, even if a state feels no moral compulsion to exclude involuntary testimonial evidence, it will still do so out of a sense of legal obligation.9
In addition to constituting customary international law, the prohibition against admitting involuntary statements is also rooted in international treaties. Article 38(1) of the Statute of the International Court of Justice offers a quasihierarchy of the sources of international law; while it does not elevate treaties explicitly, it does give them priority in its list of sources.10 Treaties are also widely recognized by scholars as a valid source of international law that may in some circumstances be superior to custom, when treaties can more clearly reflect the parties' specific intentions.11 In this instance, treaties …