76 midst of the crisis, ha[ve] been able to overcome such problems and implement the new penal model –in form and content.” 148. Regarding these allegations by Paraguay (supra paras. 145 and 147), the Court reiterates that, as stipulated in Article 27 of the Vienna Convention on the Law of Treaties, it is a basic principle of international law that “[a] party may not invoke the provisions of its internal law as justification for its failure to perform a treaty.” In international law, a customary norm establishes that a State which has ratified a human rights treaty must introduce the necessary modifications to its domestic law to ensure proper compliance with the obligations it has assumed.144 States may not fail to comply with these treaty-based obligations by invoking alleged difficulties of a domestic nature.145 Consequently, the State cannot invoke the regulation of the criminal procedure in Paraguay applied to the proceedings against Mr. Canese in order not to comply with the guarantee of reasonableness in the time required to judge the alleged victim, in accordance with its obligation established in Article 8(1) of the American Convention. 149. The Court has also established that the Constitutional Chamber of the Supreme Court of Justice of Paraguay took almost three years to decide the action on unconstitutionality filed by Mr. Canese on November 19, 1997, against the judgments of first and second instance. It should be noted that, in this decision, the Constitutional Chamber declared that the “legal action had extinguished,” even though Mr. Canese and his lawyer had requested six times146 that this action on unconstitutionality be decided. 150. Furthermore, the decision of the Criminal Chamber of the Supreme Court of Justice of Paraguay of December 11, 2002 (supra para. 69(49)), which absolved Canese, stated that: The accused should be protected effectively by delivering a final judgment in this instance, because this criminal case has been processed before all the judicial instances for almost ten years and, according to Article 8 of the said American Convention, “Every person has the right to a hearing, with due guarantees and within a reasonable time.” 151. Based on the foregoing considerations, and on a comprehensive examination of the criminal proceedings filed against Mr. Canese, this Court concludes that the State violated the right of Mr. Canese to a hearing, within a reasonable time, in violation of the provisions of Article 8(1) of the American Convention. b) Regarding the right to presumption of innocence 152. Article 8(2) of the American Convention establishes that: 144 Cf. Case of Juan Humberto Sánchez. Interpretation of judgment on preliminary objections, merits and reparations. (Art. 67 American Convention on Human Rights). Judgment of November 26, 2003. Series C No. 102; para. 60; Case of Bulacio. Judgment of September 18, 2003. Series C No. 100, para. 117; and Case of Barrios Altos. Intepretation of the judgment on merits. (Art. 67 American Convention on Human Rights). Judgment of September 3, 2001. Series C No. 83, para. 17. 145 Cf. Case of Bulacio, supra note, para. 144; Case of Trujillo-Oroza. Reparations (Art. 63(1) American Convention on Human Rights). Judgment of February 27, 2002. Series C No. 92, para. 106; and Case of Barrios Altos. Judgment of March 14, 2001. Series C No. 75, para. 41. 146 Mr. Canese and his lawyer submitted requests to the Supreme Court of Justice of Paraguay on June 7, September 13, October 26 and December 9, 1999, and also February 2 and 16, 2000.