50 serious, impartial, and effective investigation." Such investigations should be carried out with all available means and should be designed to establish the truth and to investigate, prosecute, and punish all those responsible.”360 185. The Court further rules that "[i]t is possible to consider the State responsible for cruel, inhumane, or degrading treatment suffered by a person who has been in the custody of State agents, or who has died in such circumstances if, in addition, the authorities have not conducted a serious investigation of the facts followed by the prosecution of those who appear to be responsible for them." 361 In this regard, it is incumbent on the State "to provide an immediate, satisfactory, and convincing explanation of what happened to a person who was under State custody and to rebut the allegations of its responsibility, through the use of appropriate evidentiary means.”362 186. As the Inter-American Court has found, the duty to investigate must be assumed by the State as its own legal duty and be undertaken in a serious manner and not as a mere formality preordained to be ineffective,363 or as a step taken by private interests that depends upon the initiative of the victim or his family or upon their offer of proof.364 187. In the same vein, the case law of the European Court of Human Rights holds that the State has the obligation to offer a "convincing explanation" of any injury sustained by someone deprived of their liberty. It has also held that where an individual makes a "credible assertion" that his rights have been infringed at the hands of agents of the State, there should be an effective official investigation. If this were not the case, it would be possible for agents of the State to abuse the rights of those within their control with virtual impunity.365 188. The fact that no one has been convicted in the case or that, despite the efforts made, it was impossible to establish the facts does not constitute a failure to fulfill the obligation to investigate. However, in order to establish in a convincing and credible manner that this result was not the product of a mechanical implementation of certain procedural formalities without the State genuinely seeking the truth, the State must show that it carried out an immediate, exhaustive and impartial investigation. 366 360 I/A Court H.R., Case of Vera Vera et al. v. Ecuador. Preliminary Objection, Merits, Reparations and Costs. Judgment of May 19, 2011. Series C No. 226, par. 87. See also I/A Court H.R., César Mendoza et al. Argentina. Preliminary Objections, Merits and Reparations. Judgment of May 14, 2013. Series C, No. 260, par. 218. 361 I/A Court H.R., Case of Vera Vera et al. v. Ecuador. Preliminary Objection, Merits, Reparations and Costs. Judgment of May 19, 2011. Series C No. 226, par. 88. 362 I/A Court H.R., Case of Vera Vera et al. v. Ecuador. Preliminary Objection, Merits, Reparations and Costs. Judgment of May 19, 2011. Series C No. 226, par. 88. 363 I/A Court H.R., Velásquez Rodríguez v. Honduras. Judgment of July 29, 1988. Series C No. 4, par. 177; I/A Court H.R., Case of Cantoral-Huamaní and García-Santa Cruz v. Peru. Preliminary Objection, Merits, Reparations and Costs. Judgment of July 10, 2007. Series C No. 167, par. 131; and I/A Court H.R., Case of Zambrano-Vélez et al. v. Ecuador. Merits, Reparations and Costs. Judgment of July 4, 2007. Series C No. 166, par. 120. 364 I/A Court H.R., Velásquez Rodríguez v. Honduras. Judgment of July 29, 1988. Series C No. 4, par. 177; I/A Court H.R., Case of Zambrano-Vélez et al. v. Ecuador. Merits, Reparations and Costs. Judgment of July 4, 2007. Series C No. 166, par. 120. 365 Cfr. European Court of Human Rights, Case of Elci and others v. Turkey, (Nos. 23141 and 25091/94), Judgment of 13 November 2003, paras. 648 and 649, and Case of Assenov and others v. Bulgaria, (No. 24760/94), Judgment of 28 October 1999, para. 102. 366 IACHR, Annual Report 1997, Report 55/97, Case 11.137 (Juan Carlos Abella et al.), Argentina, par. 412. In this regard, see also: IACHR, Annual Report 1997, Report 52/97, Case 11.218 (Arges Sequeira Mangas), Nicaragua, par. 96 and 97. [54] The Inter-American Court has stated, for example, that “the American Convention guarantees everyone access to justice to enforce their rights, and the States Parties have the obligation to prevent, investigate, identify and punish the masterminds and accessories of human rights violations.” I/A Court H.R., Case of the Constitutional Court, Judgment of