cannot be assessed alone, but must be evaluated in the context of all the evidence in the proceedings,18 because they are useful to the extent that they can provide further information on the alleged violations and their consequences.19 Based on the foregoing, the Court admits the said statement, although its probative value will be considered taking into account the above-mentioned criteria and the rules of sound judicial discretion. 28. Regarding the expert opinion provided by Espartaco Martínez during the public hearing, the representative requested that the expert witness “be rejected as an expert […] because he was an [alleged] biased witness of the State who [had] tried to manipulate the opinion of the Judges with his statement.” In this regard, she noted that Mr. Martínez “emphasized that he had no knowledge of the case, [and that] he only wished to give opinions on “dogma”, but [he had been] specific in giving an opinion that concurred with the State’s position.” In addition, she indicated that Mr. Martínez had referred to issues about which “he [had] not [been] called on to declare as an expert witness, but were situations that were being examined in the case.” She also indicated that, “as noted during the hearing, Prosecutor Martínez should have facilitated ‘his notes’ on which his expert opinion was based; however, […] they were never [received].” 29. The Court considers that, apart from these general assertions, the representative has not presented grounds for the alleged bias that would indicate the existence of one of the causes for impediment established in Article 48(1) of the Rules of Procedure. As regards the alleged concurrence of the expert’s opinion with the position of the State, the Court has already established that even when the statements of the expert witnesses contain elements that support the arguments of one of the parties, this does not per se disqualify the expert.20 Lastly, regarding the conclusions of the expert that are alleged to have exceeded the purpose of his testimony, the Court reiterates that it only admits those statements that are in keeping with the purpose that was defined opportunely (supra para. 26). Based on the above, the Court admits this expert opinion to the extent that it is in keeping with the purpose required and will assess it together with the body of evidence, taking into account the observations of the representative and the rules of sound judicial discretion. 30. The representative also made observations on the testimony given during the public hearing by Elvis Ramírez, arguing that this person did “not have the medical, psychiatric or psychological qualifications to given an opinion on the subject [on which he was called to testify],” because, during the hearing, he had confirmed that he “became aware of the place of detention of the [presumed] victim […], when he was appointed […] head of the Pre-Trial Detention Center in August 2009” and, since Raúl Díaz was released in May 2010, Mr. Ramírez had only known the SEBIN Pre-Trial Detention Center during the last 10 months of the presumed victim’s detention. She also referred to supposed contradictions in this testimony, questioned the truth of certain answers given by Mr. Ramírez, and stated that “[i]n 2004, police Captain Elvis Ramírez [had been] Head of the Rapid Response Unit of the former DISIP, now SEBIN,” and that this unit had been composed of “commandos [who] ha[d] been the subject of serious reservations owing to [the alleged] violation of human rights.” 31. In this regard, the Court recalls that witnesses are governed by the obligation established in Article 51(3) of the Rules of Procedure “to speak the truth, the whole truth, and nothing but the truth” with regard to the facts and circumstances of which they are aware concerning the purpose 18 Cf. Case of Loayza Tamayo v. Peru. Merits, para. 43, and Case of Fornerón and daughter v. Argentina, para. 13. 19 Cf. Case of Radilla Pacheco v. Mexico. Preliminary objections, merits, reparations and costs. Judgment of November 23, 2009. Series C No. 209, para. 93, and Case of Fornerón and daughter v. Argentina, para. 13. 20 Cf.. Case of Radilla Pacheco v. Mexico, para. 97. 10