A Comparative Analysis of the Foundations and Scope of the Invalidity of Evidence in the Criminal Justice Systems of Iran and the United States, with Emphasis on the Legitimacy of Judicial Decisions

Abstract

The invalidity of evidence, as one of the fundamental safeguards of a fair trial, plays a decisive role in ensuring the legitimacy of judicial decisions and protecting the defendant’s rights of defense. Employing a descriptive-analytical approach and a comparative method, the present study examines the normative foundations, scope, and consequences of the invalidity of evidence in the criminal justice systems of Iran and the United States. The findings indicate that, in the United States, the “exclusionary rule” and the fruit of the poisonous tree doctrine have developed primarily on the basis of the Fourth Amendment and the requirements of due process, with the objectives of institutional deterrence and preserving judicial integrity. Accordingly, the admission or exclusion of evidence is structured through the application of causation tests, attenuation analysis, and systematic exceptions. By contrast, in the Iranian legal system, the inadmissibility of evidence obtained through torture and coercion is explicitly provided for in the Constitution and ordinary legislation and constitutes a “hard core” of protection grounded in human dignity. Nevertheless, in areas not expressly regulated—such as certain procedural violations in the acquisition of evidence and derivative evidence—analytical and relatively coherent criteria have been formulated to a lesser extent. This deficiency may result in inconsistency in judicial decision-making and diminish predictability in criminal proceedings. By proposing a five-stage analytical model for assessing the legitimacy of evidence and distinguishing between “absolute invalidity” and “relative invalidity,” this study suggests that the Iranian legal system, while preserving its constitutional foundations and the capacities of Islamic jurisprudence, should move toward systematizing the criteria governing judicial decisions concerning unlawfully obtained evidence. It concludes that strengthening analytical criteria for the invalidity of evidence, in addition to safeguarding the defendant’s rights of defense and the integrity of criminal proceedings, can enhance the institutional legitimacy of criminal justice and public confidence in judicial decisions.