The Function of Evidentiary Invalidity in Safeguarding the Defendant’s Defense Rights: A Comparative Study with Emphasis on the Conflict Between Truth-Seeking and Individual Liberties

Abstract

One of the most fundamental tensions in criminal procedure concerns the conflict between the necessity of discovering the truth and the obligation to safeguard the defendant’s individual liberties. This conflict does not constitute an absolute dichotomy; rather, it is a regulatory issue within the framework of criminal policy and human rights, and the manner in which it is addressed determines the degree of legitimacy of criminal proceedings. In this context, the rule of evidentiary invalidity is not merely a procedural rule or a procedural sanction; rather, it constitutes a normative mechanism for constraining the State’s penal power and safeguarding the defendant’s defense rights. Using a descriptive-analytical method and a comparative approach, the present study examines the function of evidentiary invalidity in the legal systems of Iran and the United States. The findings indicate that, in the United States, the exclusionary rule governing unlawfully obtained evidence and the “fruit of the poisonous tree” doctrine have developed primarily on the basis of the Fourth Amendment and the doctrine of due process, and have been formulated with the objectives of institutional deterrence and preventing judicial complicity in constitutional violations. In contrast, within the Iranian legal system, the inadmissibility of evidence obtained through torture or coercion is explicitly stipulated in the Constitution and ordinary legislation and is grounded in human dignity and the absolute prohibition against interference with free will (Constitution of the Islamic Republic of Iran, art. 38; Code of Criminal Procedure, art. 60). Nevertheless, in areas not expressly regulated—such as certain procedural violations in the collection of evidence and derivative evidence—analytical and relatively coherent criteria have been formulated to a lesser extent. By proposing a three-level model of the functions of evidentiary invalidity—individual, institutional, and social—and introducing the criterion of a “fundamental violation of defense rights” as the standard for determining evidentiary invalidity, this article argues that evidentiary invalidity should not be analyzed as being in opposition to truth-seeking, but rather within the framework of the concept of “legitimate truth.” Accordingly, strengthening an analysis-oriented approach in Iranian law can enhance the predictability of judicial decision-making and the institutional legitimacy of criminal proceedings while preserving the effectiveness of criminal justice.