193. This Court also notes that there is no record that Azul Rojas Marín was told that the medical examination could be performed by someone of the sex she preferred. Also, the deputy prosecutor was present during the examination,252 with no record that the presumed victim had consented to this.253 B.2.c Omissions in obtaining evidence and in the investigation of possible discriminatory motives 194. To guarantee the effectiveness of investigations into human rights violations, it is necessary to avoid omissions in obtaining evidence and in following up on logical lines of investigation.254 The Court has indicated the guidelines that must be observed in criminal investigations into human rights violations and these may include: recovering and preserving probative elements in order to aid any potential criminal investigation of those responsible; identifying possible witnesses and obtaining their statements, and determining the cause, manner, place and time of the act investigated. It is also necessary to conduct a thorough investigation of the scene of the crime, and ensure that rigorous analyses are conducted by competent professionals using the most appropriate procedures, 255 and this involves guaranteeing the proper chain of custody. 195. In the instant case, the Court notes that evidence was not secured in the areas where the presumed victim said she had been in the Casa Grande Police Station; nor was the immediate custody required of key evidence, including the clothing that Ms. Rojas Marín was wearing at the time and the rubber baton involved in the incident. Even though both items underwent biological testing, they were only handed in on February 29, 2008,256 so that there is no certainty that evidence was preserved on them. 196. The Court also considers that when violent acts, such as torture, are investigated, the State authorities have the obligation to take all reasonable measures to discover whether there are possible discriminatory motives. 257 This obligation means that when there are specific indications or suspicions of violence based on discrimination, the State must do everything reasonable, according to the circumstances, to collect and secure the evidence, use all practical means to discover the truth, and issue fully reasoned, impartial and objective decisions, without omitting suspicious facts that could indicate violence based on discrimination.258 The authorities’ failure to investigate possible discriminatory motives may, On this point, the prosecutor stated that he entered the doctor’s office at the explicit invitation of the forensic physician. Cf. Report signed by the Superior Prosecutor, Head of the Decentralized Office of Internal Control of La Libertad and Santa of July 24, 2009 (evidence file, folio 2801). See also, Statement made by Azul Rojas Marín at the public hearing on merits before the Inter-American Commission on December 1, 2016. 252 Cf. Statement made by Azul Rojas Marín before the Superior Prosecutor, Head of the Decentralized Office of Internal Control of La Libertad and Santa on May 25, 2009 (evidence file, folio 199), and Statement of witness Víctor Álvarez at the public hearing on August 27, 2019. 253 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, and Case of Gómez Virula et al. v. Guatemala. Preliminary objection, merits, reparations and costs, supra, para. 77. 254 Cf. Case of Juan Humberto Sánchez v. Honduras. Preliminary objection, merits, reparations and costs, supra, para. 128, and Case of Gómez Virula et al. v. Guatemala. Preliminary objection, merits, reparations and costs, supra, para. 73. 255 Cf. Record of reception dated February 29, 2008 (evidence file, folio 2195), and Report presented by the Peruvian State to the Commission on March 24, 2014 (evidence file, folio 354). 256 Similarly see, ECHR, Case of Identoba and Others v. Georgia, No. 73235/12 [Fourth Section]. Judgment of October 7, 2014, para. 67. Similarly see, Case of Véliz Franco et al. v. Guatemala. Preliminary objections, merits, reparations and costs. Judgment of May 19, 2014. Series C No. 277, para. 208. 257 Similarly see, ECHR, Case of Nachova and Others v. Bulgaria, No. 43577/98 and 43579/98 [Grand Chamber]. Judgment of July 6, 2005, para. 160, and ECHR Case of Identoba and Others v. Georgia, No. 73235/12 [Fourth 258 52