under its custody. 200 In its case-law, this Court has also established that whenever a person is arrested in a normal state of health and subsequently appears with health problems, the State must provide a credible explanation for that situation. 201 Consequently, under this assumption, the State must be considered responsible for the injuries shown by a person who has been in the custody of State agents. 202 In such a case, the State has the obligation to provide a satisfactory and convincing explanation of what happened and to disprove the allegations regarding its responsibility, using appropriate supporting evidence. 203 Thus, the Court emphasizes that from the evidence presented in this case, it is possible to conclude that cruel, inhuman and degrading treatment has been proved against Messrs. Cabrera and Montiel. 135. In light of the foregoing, this Court reiterates that whenever there are signs that torture has taken place, the State must initiate, ex officio and immediately, an impartial, independent and thorough investigation that makes it possible to determine the nature and origin of the injuries observed, identify those responsible and begin their prosecution. 204 It is essential that the State act diligently to prevent acts of torture or cruel, inhuman and degrading treatment, bearing in mind that the victim usually refrains from denouncing such actions through fear. Similarly, the judicial authorities have a duty to guarantee the rights of the detainee, which implies obtaining and protecting any evidence that may prove alleged acts of torture. 205 The State must also guarantee the independence of the medical and health care personnel responsible for examining and providing assistance to those who are detained so that they can freely carry out the necessary medical assessments, respecting the standards established for their professional practice. 206 136. At the same time, the Court wishes to emphasize that whenever a person alleges, within a proceeding, that his statement or confession was obtained under duress, the State party has the obligation to ascertain the veracity of such complaint 207 by means of a diligent investigation. Likewise, the burden of proof cannot rest with the plaintiff, but rather it is up to the State to prove that the confession was made voluntarily. 208 200 Cf. Case of López Álvarez V. Honduras. Merits, Reparations and Costs. Judgment of February 1, 2006. Series C N° 141, paras. 104 to 106; Case of the Miguel Castro Castro Prison v. Peru. Merits, Reparations and Costs. Judgment of November 25, 2006. Series C N° 160, para. 273; Case of Ibsen Cárdenas and Ibsen Peña v. Bolivia, supra note 30, para. 117. 201 Cf. Case of Juan Humberto Sánchez v. Honduras, supra note 119, para. 100; and Case of Bulacio v. Argentina, supra note 123, para. 127. 202 Cf. Case of the “Street Children” (Villagrán Morales et al) v. Guatemala; supra note 29, para. 170; and Case of Escué Zapata v. Colombia, supra note 53, para. 71; Case of Ibsen Cárdenas and Ibsen Peña v. Bolivia, supra note 30, para. 95. 203 Cf. Case of Juan Humberto Sánchez v. Honduras, supra note 119, para. 111, Case of the Miguel Castro-Castro Prison v. Peru. Merits, Reparations and Costs. Supra note 200, para. 273; and Case of Zambrano Vélez et al. v. Ecuador, supra note 24, para. 108. 204 Cf. Case of Gutiérrez Soler v. Colombia. Merits, Reparations and Costs. Judgment of September 12, 2005. Series C No. 132, para. 54; Case of Bayarri v. Argentina, supra note 123, para. 92; Case of Bueno Alves v. Argentina. Merits, Reparations and Costs. Judgment of May 11, 2007. Series C No. 164, para. 88. 205 Cf. Istanbul Protocol, supra note 149, para. 76. 206 Cf. Istanbul Protocol, supra note 149, para. 56, 60, 65 and 66. 207 Cf. United Nations. Committee Against Torture. PE v. France. Communication 193/2001, Report of November 21, 2002, para. 6.3. 208 The Sub-committee on Prevention of Torture has stated that: “As to the assessment of evidence, it falls upon the State to prove that its agents and institutions do not commit acts of torture and it is not for the victim to prove that acts of torture have taken place, specially when the victim has 53