63 proof.214 In light of this obligation, once State authorities are aware of an incident, they should initiate ex officio and without delay, a serious, impartial, and effective investigation.215 This investigation must be carried out using all available legal means with the aim of discovering the truth. 192. The Court has also indicated that Article 8 of the Convention reveals that the victims of human rights violations, or their next of kin, should have wideranging possibilities of being heard and taking part in the respective proceedings, both in order to clarify the facts and punish those responsible, and also to seek due reparation. Furthermore, the Court has indicated that the obligation to investigate and the corresponding right of the alleged victims or the next of kin is not only evident from the treaty-based provisions of international law that are binding for the State Parties, but also arise from domestic law regarding the obligation to investigate ex officio certain unlawful conduct, as well as from the norms that permit the victims or their next of kin to denounce or submit complaints, evidence or petitions, or take any other measure in order to play a procedural role in the criminal investigation in order to establish the truth of the facts.216 193. In cases of violence against women, the general obligations established in Articles 8 and 25 of the American Convention are complemented and enhanced by the obligations arising for States parties from a specific Inter-American treaty, the Convention of Belem do Pará. Article 7(b) of this Convention specifically obliges the States parties to apply due diligence to prevent, punish and eradicate violence against women. Thus, when an act of violence against a woman occurs, it is particularly important that the authorities in charge of the investigation conduct it in a determined and effective manner, taking into account society’s obligation to reject violence against women and the State’s obligation to eliminate it and to ensure that victims have confidence in the State institutions for their protection. 194. On other occasions, this Court has defined the guiding principles that must be observed in criminal investigations into human rights violations, and these may include, inter alia: recovery and preservation of probative material in order to assist in any potential criminal investigation of the authors; identification of possible witnesses and obtaining their statements, and determination of the cause, form, place and time of the act investigated. In addition, the scene of the crime should be examined thoroughly, and rigorous tests should be performed by competent professionals, using the most appropriate procedures.217 In cases of violence against women, several international instruments describe and illustrate the enhanced State obligation to investigate them with due diligence.218 Among 214 Cf. Case of Velásquez Rodríguez. para, supra note 27, para. 177; Case of Radilla Pacheco, supra note 33, paras. 192 and 233, and Case of Chitay Nech et al., supra note 18, para. 192. 215 Cf. Case of the Pueblo Bello Massacre v. Colombia. Merits, Reparations, and Costs. Judgment of January 31, 2006. Series C No. 140, para. 143; Case of Perozo et al., supra note 46, para. 298, and Case of González et al., (“Cotton Field”), supra note 15, para. 290. 216 Cf. As an example, the Federal Code of Criminal Procedure, Article 141, which recognizes the Rights of the injured party in the preliminary investigation (section A), in the criminal procedure (section B), and during the execution of punishments (section C), and the Criminal Procedure Code of the state of Guerrero, Article 5, first paragraph, which recognizes the right of the victim or the injured party to contribute to the Public Prosecutor, offering the judge, by way of conduct or directly, all the facts available to prove the assertions and amount of harm and detriment caused by the crime. 217 Cf. Case of Juan Humberto Sánchez v. Honduras. Preliminary Exceptions, Merits, Reparations, and Costs. Judgment of June 7, 2003. Series C No. 99, para. 128; Case of Garibaldi, supra note 195, para. 115, and Case of González et al., (“Cotton Field”), supra note 15, para. 300. 218 Cf. United Nations Office of the High Commissioner for Human Rights, Istanbul Protocol, supra note 36, inter alia, paras. 67, 77, 89, 99, 101 to 103, 155, 162, 163, 170, 171, 224, 225, 260, 269, and 290, and W.H.O., Guidelines for medico-legal care for victims of sexual violence, supra note 36, inter alia, pages 17, 30, 31, 34, 39 to 44, and 57 to 74.