85 against women. 402 In such cases, the State authorities must open ex officio and immediately, a serious, impartial and effective investigation as soon as they become aware of the facts that constitute violence against women, including sexual violence. 403 Thus, when an act of violence has been perpetrated against a woman, it is particularly important that the authorities in charge of the investigation conduct this with determination and effectiveness, bearing in mind the duty of society to reject violence against women, and the State’s obligation to eradicate this and to inspire confidence in the victims in the States institutions created to protect them. 404 242. The Court has specified the guiding principles that must be observed in criminal investigations involving human rights violations. 405 The Court has also indicated that the obligation to conduct an effective investigation has added implications when a woman has died or suffered ill-treatment or restriction of her personal liberty in the context of generalized violence against women. 406 In cases of violence against women, various international instruments are useful for specifying and providing content to the enhanced State obligation to investigate them with due diligence. 407 Among other matters, a criminal investigation into sexual violence must: (i) document and coordinate the investigation procedures and process the evidence diligently, taking sufficient specimens, performing tests to determine the possible perpetrator of the act, preserving other evidence such as the victim’s clothes, inspecting the scene of the incident immediately, and ensuring the proper chain of custody; (ii) provide free legal assistance to the victim during all stages of the proceedings, and (iii) provide both emergency and, if necessary, continuing medical, prophylactic and psychological care to the victim, using a treatment protocol aimed at lessening the consequences of the offense. 408 Also, 402 Cf. Case of Fernández Ortega et al. v. Mexico, supra, para. 193, and Case of Veliz Franco et al. v. Guatemala, supra, para. 185. 403 Cf. Case of the Miguel Castro Castro Prison v. Peru, supra, para. 378, and Case of Veliz Franco et al. v. Guatemala, supra, para. 185. 404 Cf. Case of Fernández Ortega et al. v. Mexico, supra, para. 193, and Case of Veliz Franco et al. v. Guatemala, supra, para. 185. 405 These may include, inter alia: to gather and preserve the evidence in order to contribute to any potential criminal investigation of those responsible; to identify possible witnesses and to obtain their statements, and to determine the cause, form, place and time of the fact investigated. In addition, it is necessary to conduct a thorough investigation of the scene of the crime, and ensure that a rigorous analysis is made by competent professionals, using the most appropriate procedures. Cf. Case of Juan Humberto Sánchez v. Honduras, supra, para. 128, and Case of J. v. Peru, supra, para. 344. 406 Cf. Case of González et al. (“Cotton Field”) v. Mexico. Preliminary objection, merits, reparations and costs. Judgment of November 16, 2009. Series C No.205, para. 293, and Case of Veliz Franco et al. v. Guatemala, supra, para. 186. 407 Cf. Case of Fernández Ortega et al. v. Mexico, supra, para. 194, and Case of J. v. Peru, supra, para. 344. Istanbul Protocol, 2001, paras. 67, 77, 89, 99, 101 to 105, 154, 161 to 163, 170, 171, 224, 225, 260, 269 and 290, and World Health Organization, Guidelines for medico-legal care for victims of sexual violence, Geneva, 2003, inter alia, pp. 17, 30-1, 34, 39 to 44 and 57 to 74. 408 Cf. Case of Fernández Ortega et al. v. Mexico, supra, para. 194, and Case of J. v. Peru, supra, para. 344. In this regard, the State is obliged to provide, with the consent of the victims, treatment for the consequences to their health of the sexual violence, including the possibility of access to prophylactic treatment and treatment to prevent pregnancy. In this regard, see:: World Health Organization, Guidelines for medico-legal care for victims of sexual violence, Geneva, 2003, inter alia, p. 63, Available at: http://whqlibdoc.who.int/publications/2004/ 924154628X.pdf?ua=1; See also: Instrumento de Trabajo y Consulta, Protocolo Interinstitucional de Atención Integral a Víctimas de Violación Sexual (Costa Rica), Available at: http://ministeriopublico.poder-judicial.go.cr/biblioteca/ protocolos/10.pdf; Modelo Integrado para la Prevención y Atención de la Violencia Familiar y Sexual, 2010 (Mexico), Available at: http://www.inm.gob.mx/static/Autorizacion_Protocolos/SSA/ModeloIntregrado_para_Prevencion_Atn_ Violencia_familiar_y_se.pdf; Federación Latinoamericana de Sociedades de Obstetricia and Ginecología, Propuesta de Estándares Regionales para la Elaboración de Protocolos de Atención Integral Temprana a Víctimas de Violencia Sexual (2011), Available at: http://www.flasog.org/wp-content/uploads/2014/01/Propuestas-Estandares-ProtocolosAtencion-Victimas-Violencia-FLASOG-2011.pdf; Modelo de Atención Integral en Salud para Víctimas de Violencia http://www.minsalud.gov.co/Documentos%20y%20Publicaciones/ Sexual, 2011 (Colombia) Available at: MODELO%20DE%20ATENCI%C3%93N%20A%20V%C3%8DCTIMAS%20DE%20VIOLENCIA%20SEXUAL.pdf, and Guía Técnica de Atención Integral de Personas Afectadas por la Violencia basada en Género, 2007 (Peru), Available at: http://www.sis.gob.pe/ipresspublicas/ normas/pdf/minsa/GUIASPRACTICAS/2007/RM141_2007.pdf .