43 Public Attorneys, imposes on them the obligation to carry out their duties acting on the basis of the regulations defined in Constitution and statute. That way, prosecutors must watch for the law to be correctly applied and seek the truth of the facts as they are, acting professionally, loyally and in good faith”166. 134. It is appropriate to recall that in cases of forced disappearance, it is essential the prompt and immediate action of prosecution and judicial authorities, by the order of timely and necessary measures addressed to determine the whereabouts of the victim or the place where he or she could be found alive. Nevertheless, it was six years after the disappearance, in 1999, that the Prosecutor's Office ordered the forwarding of official letters, within the framework of further investigative measures, to different public institutions in order to locate the whereabouts of Mr. Anzualdo167, without obtaining any result, since the required institutions did not send any response to the authorities charged with the investigation and there is no evidence of any reiteration168. Later on, the Prosecutor’s Office requested that the proceedings continue since up to that moment “it [has been] not possible to determine the whereabouts”169. 135. In this regard, this Tribunal has established that in order to conduct an effective and expedious investigation, the investigating body must use all the means at its disposal to carry out all measures and investigations necessary to shed light on the fate of the victims and identify the responsible for the forced disappearance170. For this, the State will guarantee that the authorities in charge of the investigation have the logistic and scientific resources necessary to collect and process evidence, and more specifically, the power to access to the documents and information relevant to the investigation of the facts denounced and that they be able to obtain evidence of the locations of the victims171. Furthermore, it is fundamental that the investigating authorities have unrestricted access to detention centers, regarding the 166 Cf. Case of Tristán Donoso V. Panamá. Preliminary Objection, Merits, Reparations and Costs. Judgment of January 27, 2009. Series C No. 193, para. 165. 167 It was requested to the Identification and Marital Status Record Office of Lima, to forward the registration of Kenneth Ney Anzualdo Castro together with his date and photograph in order to collect information about a possible recent registration in some part of the country; it was requested to the Callao Harbormaster’s Office information regarding the discovery of a corpse in the Peruvian coast; it was requested to the Bureau of Immigration and Naturalization information of any possible migratory movement of Kenneth Ney Anzualdo Castro; it was requested to the Directorate of State Security of PNP [National Police of Peru] and to the National Antiterrorism Bureau of PNP information regarding the possible detention of Kenneth Ney Anzualdo Castro. There was no response whatsoever. Cf. Report N. 337-DPMP-DIVPOLJUD-JPPC of September 14, 1999 (record of evidence, volume V, appendix 11 to the application, pages 1755-1756). 168 See Report N. 337-DPMP-DIVPOLJUD-JPPC of September 14, 1999 (record of evidence, volume V, appendix 11 to the application, pages 1755-1756). 169 Order of the Office of the Fifth Provincial Prosecutor for Criminal Matters of Callao, of September 15, 1999 (record of evidence, volume V, appendix 11 to the application, page 1759). 170 Cf. Case of Velásquez Rodríguez V. Honduras. Merits, supra note 11, para. 174; Case of Tiu Tojín V. Guatemala., supra note 59, para . 77; Case of Heliodoro Portugal V. Panama, supra note 58; para. 144; Case of García Prieto et al. V. El Salvador. Preliminary Objection, Merits, Reparations and Costs. Judgment of November 20, 2007. Series C No. 168, para. 101; Case of the Serrano Cruz Sisters V. El Salvador. Merits, Reparations and Costs; supra note 90, para. 83. See also, Article X of the InterAmerican Convention on Forced Disappearance of Persons and Article 12 of the International Convention on the Protection of All People from Enforced Disappearance. 171 Case of Tiu Tojín V. Guatemala., supra note 59, para . 77. See also, Article X of the InterAmerican Convention on Forced Disappearance of Persons and Article 12 of the International Convention on the Protection of All People from Enforced Disappearance.