54 and progress of the procedure.202 In the instant case, given the analysis of the effectiveness of the investigations carried out, the Court takes into account the context in which the detention and subsequent disappearance of Messrs. Rainer Ibsen Cárdenas and José Luis Ibsen Peña are framed. To this end, at the public hearing (supra para. 8), the State indicated that “[i]t had to assume the responsibility of acknowledging the human rights violations committed by a dictatorial regime that marked a dark past in the history of Bolivia [,] which lasted from the coup d’etat led by then Colonel Hugo Banzer Suárez in 1971, to the year 1982, in which the [State of Bolivia] returned to democracy.” 166. In this line of thought, the Court considers, in this type of cases, that the authorities in charge of the investigations had the duty to guarantee that throughout the course of the same the systematic patters that permitted the perpetration of serious human rights violations in the present case would be assessed.203 In seeking to guarantee its effectiveness, the investigation should have been carried out taking into account the complexity of this type of facts and the structure in which the people probably involved are located, pursuant to the context in which they occurred, thus avoiding omissions in the gathering of evidence and in the follow-up of the logical lines of investigation.204 167. This Tribunal has already indicated that in cases of forced disappearance, it is essential that the judicial authorities and the Public Prosecutor’s Office take prompt and immediate action through timely and necessary measures to determine the victim’s whereabouts.205 Likewise, the Court reiterates that the passage of time holds a directly proportional relation to the limitation –and in some cases, the impossibility- to obtain evidence and/or testimonies, hindering and even voiding or making ineffective the evidentiary procedures aimed to clarify the central facts of investigation,206 to identify possible perpetrators and participants, and to determine the possible criminal liabilities. Without detriment of the aforementioned, the national authorities are not exempt from making all efforts necessary to comply with their obligation to investigate.207 The Court has also observed that such obligation is maintained “whoever the agent to whom the violation may eventually be attributed is, even private persons, since, if their acts are not investigated seriously, they would turn out, in some way, assisted by the public power, which would compromise the State’s international responsibility.”208 202 Cf. Case of Garibaldi v. Brazil. Preliminary Exceptions, Merits, Reparations and Costs. Judgment of September 23, 2009. Series C No. 203, para. 120. 203 Cf. Case of La Rochela Massacre v. Colombia, supra note 26, para. 156; Case of Anzualdo Castro v. Peru, supra note 44, para. 154, and Case of Radilla Pacheco v. Mexico, supra note 8, para. 206. 204 Cf. Case of the Serrano-Cruz Sisters v. El Salvador. Merits, Reparations and Costs. Judgment of March 1, 2005. Series C No. 120, paras. 88 and 105; Case of Anzualdo Castro v. Peru, supra note 44, para. 154, and Case of Radilla Pacheco v. Mexico, supra note 8, para. 206. 205 Cf. Case of Anzualdo Castro v. Peru, supra note 44, para. 134, and Case of Radilla Pacheco v. Mexico, supra note 8, para. 215. 206 Cf. Case of Heliodoro Portugal v. Panamá, supra note 1, para. 150; Case of Anzualdo Castro v. Peru, supra note 44, para. 135, Case of Radilla Pacheco v. Mexico, supra note 8, para. 215. 207 Cf. Case of Radilla Pacheco v. Mexico, supra note 8, para. 215. 208 Cf. Case of Velasquez Rodriguez. Merits, supra note 14, para. 174; Case of Kawas Fernandez v. Honduras, supra note 11, para. 78, and Case of Radilla Pacheco v. Mexico, supra note 8, para. 216.