Second Court of the Criminal Appeals and Guarantees Chamber of the province of Buenos Aires decreed “the total and final dismissal of the case against [three persons] in relation to the offense of unlawful deprivation of liberty followed by death.” 232 117. In addition, in September 2004, statements were again received from the male eyewitness and the street vendor (supra para. 65), and they indicated that they had received pressure and threats from the police owing to their participation in the trial of the federal police agent indicted. 233 118. Regarding the obstructions to the proceedings, this Court has ruled that, in order to ensure due process, States must take all necessary measures to protect agents of justice, investigators, witnesses, and family members of victims from harassment and threats aimed at hindering the proceedings, avoiding the elucidation of the facts, and concealing those responsible. 234 To the contrary, those who investigate and those who could be witnesses would feel intimidated and frightened and this would have a significant impact on the effectiveness of the investigation 235 119. Added to the above, the Court has considered that the threats and intimidation suffered by witnesses in the domestic proceedings cannot be examined in isolation, but should be analyzed in the context of obstructions to the investigation of the case. Consequently, such acts become another means of perpetuating impunity and preventing the truth of what happened from being known. 236 The Court has defined impunity as “the total absence of investigation, pursuit, capture, prosecution, and sentencing of those responsible for human rights violations.” 237 120. Furthermore, the Court considers that, for an investigation to be effective, those responsible for it must be independent, from a hierarchical and institutional point of view and also in the practice, from the individuals implicated in the events investigated. 238 121. In this regard, the Court notes that, in the instant case, at least five witnesses denounced that they had been threatened or pressured by federal police agents or by family 232 Cf. Decision of June 19, 2008, in Fs. 3448/3455, Preparatory criminal investigation No. 167,253 into the murder of Commissioner Piazza (file of annexes to the pleadings and motions brief, folios 2331 and 2344). 233 The street vendor witness indicated that, in the Federal Police Unit in the Constitución Precinct, an official who used to accompany the police agent who was acquitted on the trains, asked him what he had testified in the oral proceeding and told him that he “should remember that [the police agent acquitted] was a good person and […] had not killed the Assistant Commissioner.” He also indicated that, following this, he felt pressured by the police on the trains, and he “was harassed.” Cf. Testimony of March 18, 2004, before the Special Investigative Committee of the Ministry of Security of the province of Buenos Aires (file of annexes to the pleadings and motions brief, folio 1912). The eyewitness stated, inter alia, that he was obliged to change his statement with a gun to his head. Cf. Testimony Fs. 2907/2908, Proceeding 10,888, presented on March 25, 2004 (file of annexes to the pleadings and motions brief, folios 1915 to 1918). 234 Cf. Case of Myrna Mack Chang, supra, para. 199, and Case of the La Rochela Massacre v. Colombia. Merits, reparations and costs. Judgment of May 11, 2007. Series C No. 163, para. 171. 235 Cf. Case of Kawas Fernández, supra, para. 106, and Case of Luna López, supra, para. 173. 236 Cf. Case of the Las Dos Erres Massacre supra, para. 145. 237 Cf. Case of the “White Van” (Paniagua Morales et al.) v. Guatemala. Merits, supra, para. 173, and Case of the Las Dos Erres Massacre, supra, para. 234. 238 Cf. Case of Baldeón García v. Peru. Merits, reparations and costs. Judgment of April 6, 2006. Series C No. 147, para. 95. See also, ECHR, Case of Giuliani and Gaggio v. Italy, Judgment of 24 March 2011, para. 300: “For an investigation into alleged unlawful killing by State agents to be effective, it may generally be regarded as necessary for the persons responsible for and carrying out the investigation to be independent from those implicated in the events (see, for example, Güleç, cited above, §§ 81-82, and Oğur, cited above, §§ 91-92). This means not only a lack of hierarchical or institutional connection but also a practical independence.” 46