133. As has been the practice of both the Commission208 and the Court,209 when dealing with a violent death, the "United Nations Manual on the Effective Prevention and Investigation of Extra-Legal, Arbitrary and Summary Executions,"210 is a useful tool to assess the steps taken by investigative authorities, especially in the first stages. This is the case because the above-mentioned instrument recapitulates the minimum--that is, the most basic--steps that must be taken “to discover the truth about the events leading to the suspicious death of a victim.211 Thus, said Manual establishes that the state authorities that carry out an investigation shall seek, inter alia: (a) to identify the victim; (b) to recover and preserve evidentiary material related to the death; (c) to identify possible witnesses and obtain statements from them concerning the death; (d) to determine the cause, manner, location and time of death, as well as any pattern or practice that may have brought about the death; and (e) to distinguish between natural death, accidental death, suicide and homicide. In addition, the scene of the crime must be searched exhaustively, and autopsies and tests of the human remains must be performed rigorously by competent professionals using the most appropriate procedures.212 134. The Commission also observes that, as established in the United Nations Manual on Extrajudicial Executions, due diligence in a medico-legal investigation of a death requires maintaining the chain of custody of each item of forensic evidence.213 In that regard, the Inter-American Court has held that: This consists in keeping a precise written record, complemented, as applicable, by photographs and other graphic elements, to document the history of the item of evidence as it passes through the hands of the different investigators responsible for the case.214 135. In this case, having analyzed the available information on the investigations carried out, the IACHR has identified a series of omissions on the part of the Public Prosecution Service after the events occurred. To begin with, the Commission finds that the State did not adequately preserve all the relevant evidence, given that there was no mention of the shell casings collected in the records of the proceeding. There is also information indicating that the victims' clothing was lost. 136. Second, the IACHR finds that the State also did not preserve the scene of the crime adequately. The Commission notes that the petitioners claimed that the police did not cordon off the area where the events occurred, which allowed people to transit through it. The IACHR observes that the State has not contested those submissions. Third, the Commission takes note of what the CEH said with regard to the autopsies carried out on the deceased, to the effect that they were "superficially performed without meeting the proper technical requirements.” 208 See IACHR, Report No. 48/97, Case 11.411, Merits, Severiano and Hermelindo Santiz Gómez “Ejido Morelia”, Mexico, February 18, 1998; Report No. 34/00, Case 11.291, Merits, Carandirú, Brazil, April 13, 2000; Report No. 1/98, Case 11.543, Merits, Rolando Hernández-Hernández, Mexico, May 5, 1998; Report No. 10/95, Case 10.580, Admissibility and Merits, Manuel Stalin Bolaños, Ecuador, September 12, 1995. 209 I/A Court H.R., Case of González et al. (“Cotton Field”) v. Mexico. Preliminary Objection, Merits, Reparations and Costs. Judgment of November 16, 2009. Series C No. 205, par. 301; and Case of the Miguel Castro-Castro Prison v. Peru. Merits, Reparations and Costs. Judgment of November 25, 2006. Series C No. 160, par. 383. 210 United Nations Manual on the Effective Prevention and Investigation of Extra-Legal, Arbitrary and Summary Executions, adopted by the United Nations General Assembly in 1991. U.N. Document ST/CSDHA/12. 211 United Nations Manual on the Effective Prevention and Investigation of Extra-Legal, Arbitrary and Summary Executions, adopted by the United Nations General Assembly in 1991. U.N. Document ST/CSDHA/12, para. 9. 212 I/A Court H.R., Case of Servellón García et al. v. Honduras. Judgment of September 21, 2006. Series C No. 152, par. 120. United Nations Manual on the Effective Prevention and Investigation of Extra-Legal, Arbitrary and Summary Executions. See, also, I/A Court H.R., Case of González et al. (“Cotton Field”) v. Mexico. Preliminary Objection, Merits, Reparations, and Costs. Judgment of November 16, 2009. Series C No. 205, par. 305. 213 214 I/A Court H.R., Case of González et al. (“Cotton Field”) v. Mexico. Preliminary Objection, Merits, Reparations, and Costs. Judgment of November 16, 2009. Series C No. 205, par. 305. 30