35 impossibility of the complainant to procure evidence, when it is the State that controls the means of clarifying facts that occurred on its territory.123 128. The Court has no evidence of the content of all the intercepted telephone conversations and the individuals involved, because the transcripts of the recorded material were not provided to the case file of the monitoring petitions (despite the provisions of Article 6 of Law No. 9,296/96), or to the file of the instant case. Consequently, the Court finds it reasonable to grant probative value to the evidence arising from the case file. Bearing in mind, therefore, the duration of the telephone monitoring and the role played in the organizations by Delfino José Becker and Pedro Alves Cabral who, at the time of the facts were, respectively, a COANA Board member and the President of ADECON,124 it is very possible that their communications were intercepted. Thus, even though it is not possible to prove the interception directly and with total certainty, the Court concludes that there was also interference in the private live of Delfino José Becker and Pedro Alves Cabral. 129. Since the telephone conversations of the alleged victims were private and they had not authorized that their conversations be conveyed to third parties, the interception of the conversations by State agents constituted interference in their private life. Therefore, the Court must examine whether this interference was arbitrary or abusive in the terms of Article 11(2) of the Convention or whether it was compatible with the said treaty. As indicated previously (supra para. 116), to conform to the American Convention any interference must comply with the following requirements: (a) it must be established by law; (b) it must have a legitimate purpose, and (c) it must be appropriate, necessary and proportionate. Consequently, the absence of any of these requirements implies that the interference is contrary to the Convention. (a) Legality of the interference 130. The first step to evaluate whether a right established in the American Convention can be adversely affected in light of that treaty consists in examining whether the questioned measure complies with the requirement of legality. This means that the general conditions and circumstances under which a restriction to the exercise of a specific human right is authorized must be clearly established by law.125 The norm that establishes the restriction must be a law in the formal and substantial sense.126 131. Taking into account that telephone interception can represent a serious interference in the private life of an individual, this measure must be based on a law that must be precise and indicate the corresponding clear and detailed rules,127 such as the circumstances in which this measure can be adopted, the persons authorized to request it, to order it and to carry it out, and the procedure to be followed. 123 Cf. Case of Velásquez Rodríguez, supra note 54, para. 135; Case of Ríos et al., supra note 18, para. 98, and Case of Kawas Fernández, supra note 35, para. 95. 124 Cf. Minutes of the third General Assembly of COANA of March 13, 1999, supra note 71, folios 1021, 1039 and 1068, and Testimony of Delfino José Becker rendered before notary public on November 7, 2008, supra note 72, folio 968. 125 Article 30 of the American Convention establishes: The restrictions that, pursuant to this Convention, may be placed on the enjoyment or exercise of the rights or freedoms recognized herein may not be applied except in accordance with laws enacted for reasons of general interest and in accordance with the purpose for which such restrictions have been established. 126 Cf. The Word "Laws” in Article 30 of the American Convention on Human Rights. Advisory Opinion OC-6/86 of May 9, 1986. Series A. No. 6, paras. 27 and 32, and Case of Tristán Donoso, supra note 9, para. 77. 127 ECHR. Case of Kruslin v. France, judgment of 24 April 1990, Series A, No. 176-A, para. 33, and Case of Huvig v. France, judgment of 24 April 1990, Series A No. 176-B, para. 32.