counterinsurgency operations by the Armed Forces, and the structure in which the persons who are probably involved were inserted, thus avoiding omissions in the collection of evidence and in following logical lines of investigation.407 In this regard, the Court considers that State authorities are obliged to collaborate in the collection of evidence in order to achieve the objectives of the investigation and must abstain from actions that entail obstructions to the progress of the investigative process.408 It is also essential that the organs responsible for the investigations be provided, formally and substantially, with the adequate and necessary authority and guarantees to obtain access to the pertinent documentation and information to investigate the facts denounced and obtain indications or evidence of the location of the victims.409 The State cannot shield itself behind lack of evidence of the existence of the documents requested; but rather, it must justify the refusal to provide them, demonstrating that it has taken all available measures to verify that the information requested does not exist.410 Thus, in the case of human rights violations the Court has already indicated that “State authorities cannot shield themselves behind mechanisms such as State secrets or the confidentiality of information, or by reasons of public interest or national security, in order not to provide the information required by the judicial or administrative authorities responsible for the pending investigation or proceedings.”411 258. Second, the Court observes that although the trial judge ordered the inspection of the scene of the events and the exhumation of the corpses on November 9, 1990, it was not until June 19, 1991, that the judge established the date for this measure that, finally, was not carried out due to insufficient time to prepare for it according to the letter from the Director of the Institute for Forensic Medicine (supra para. 215). Subsequently, it was not possible to perform the required exhumations owing to the supposed existence of mines in the area where the measure ordered was to be carried out. This situation persisted until May 5, 1992, when the trial judge ordered that the measures should continue (supra paras. 217 to 226). Finally, it was only on May 27, 1992, that the inspections of the places where the events occurred took place, and on September 9, 1992, that the first exhumations were authorized, which were performed from October 13 to November 17, 1992 (supra paras. 227 and 230). In other words, even though Pedro Chicas Romero’s initial complaint was filed on October 26, 1990, it was only on October 13, 1992, that the first exhumations were performed. Thus, for almost two years no exhumation work was performed owing to the lack of experts in this area and the supposed existence of mines; situations which were used to justify the inactivity of the judicial authority. 259. According to the internal reports of Tutela Legal del Arzobispado, in a meeting between this organization and the trial judge on March 27, 1992, the latter stated that “he had received orders from above to delay the investigation or to bring it to a standstill”; these orders came from the President of the Republic, the President of the Supreme Court of Justice, the Prosecutor General, and even the Minister of Defense at the time. These orders were, inter alia, that he should not establish a date for the exhumations.412 Also, in a press communiqué of April 8, 1992, Tutela Legal del Arzobispado denounced irregularities that it believed were being committed in the investigations up until that time. These irregularities included that the trial judge had refused “to indicate [to the members of the Argentine Forensic Anthropology Team] a date for the inspection and exhumation, [giving] credibility to the rumors of minefields in the 407 Cf. Case of the Serrano Cruz Sisters v. El Salvador. Merits, reparations and costs, para. 166, and Case of the Río Negro Massacres v. Guatemala, para. 194. 408 Cf. Case of García Prieto et al. v. El Salvador. Preliminary objections, merits, reparations and costs. Judgment of November 20, 2007. Series C No. 168, para. 112, and Case of the Río Negro Massacres v. Guatemala, para. 194. 409 Cf. Case of Tiu Tojín v. Guatemala, para. 77, and Case of Contreras et al. v. El Salvador, para. 145. 410 Cf. Case of Gomes Lund et al. (Guerrilha do Araguaia) v. Brazil, para. 211, and Case of Contreras et al. v. El Salvador, para. 177. 411 Case of Myrna Mack Chang v. Guatemala, para. 180, and Case of Contreras et al. v. El Salvador, para. 171. 412 Cf. Internal reports of the Oficina de Tutela Legal del Arzobispado of March 27 and July 29, 1992 (evidence file, tome II, annex 10 to the submission of the case, folios 1537 to 1543). 85