In 2002, Alex Lemún, a 17-year-old Mapuche youth, was shot by a police officer during a land occupation protest. It took over 20 years and tedious administrative and judicial processes for his family to gain access to justice mechanisms in Chile. Against this background, this chapter examines the Lemún case as a lens through which to understand the broader challenge of implementing decisions of the Inter-American Human Rights System in national legal systems. The chapter explores how the Chilean Supreme Court responded to the Inter-American Commission on Human Rights’ recommendation to reopen the investigation, despite the absence of a clear domestic rule permitting such action and analyses the jurisprudential developments that made this response possible. More broadly, this chapter addresses a recurring legal problem in Chile: the reopening of criminal proceedings in cases of serious human rights violations that were previously dismissed by national courts, often under amnesty or statute of limitations rules and examines how the Chilean Supreme Court has dealt with situations of interested denial of justice, particularly when recognised by international human rights bodies. The work deeps on the Lemún case as a vehicle for exploring how the Chilean judiciary has contributed to the construction of a legal doctrine that denies legal effects to judicial decisions adopted in contexts of systematic denial of justice. Finally, the chapter also reflects on the legal status of this emerging legal doctrine and the challenges it raises for legal certainty, especially with regard to the interpretation of statute of limitations and res judicata rules in inter-legal contexts.