223. In addition, Article 1(b) of the Inter-American Convention on Forced Disappearance of Persons imposes on States the obligation “[t]o punish within their jurisdictions, those persons who commit or attempt to commit the crime of forced disappearance of persons and their accomplices and accessories.” Therefore, in keeping with this Court’s case law, in the case of a forced disappearance, States have the duty to launch an investigation ex officio. Thus, “whenever there is sufficient reason to suspect that a person has been subjected to a forced disappearance, an investigation must be opened. This obligation is irrespective of whether a complaint has been file because, in cases of forced disappearance, international law and the general obligation of guarantee impose the obligation to investigate the case ex officio, without delay, and in a serious, impartial and effective manner. This is a fundamental and decisive element for the protection of the rights affected by these situations, such as personal liberty, personal integrity and life. Furthermore, any State authority, public official or private individual who has heard of actions aimed at the forced disappearance of persons must report this immediately.”303 Consequently, the investigation must be conducted using all legal means available in order to determine the truth, as well as to pursue, capture, prosecute and eventually punish all the masterminds and the perpetrators of the facts, especially when State agents are or could be involved.304 224. In addition, in cases of forced disappearance, the investigation will have certain specific connotations that arise from the very nature and complexity of the phenomenon under investigation; in other words, the investigation must also include taking all necessary measures to determine the fate of the victim and his or her whereabouts.305 The Court has already clarified that the obligation to investigate facts of this nature persists as long as the uncertainty about the final fate of the disappeared person remains, because the right of the victim’s next of kin to know his or her fate and, as appropriate, where the victim’s remains are, represents a reasonable expectation that the State must satisfy using all the means at its disposal.306 225. In addition, since protection from slavery and involuntary servitude is an international obligation erga omnes, derived “from the principles and rules relating to the basic rights of the human person” (supra para. 141), when States become aware of an act constituting slavery or involuntary servitude, in the terms of Article 6 of the American Convention, they must open the pertinent investigation ex officio, in order to establish the corresponding individual responsibilities. 226. In this case, the Court observes that multiple testimonies given domestically by victims who survived the massacres reveal that during the massacres, acts that presumably constitute forced disappearance and torture of members of the Río Negro community were committed, as were alleged acts of rape against the girls and women of that community. Some of this testimony was given after March 9, 1987, the date as of which this Court has jurisdiction over human rights violations recognized in the American Convention; after January 29, 1987, the date on which Guatemala ratified the Convention to Prevent and Punish Torture; after April 4, 1995, the date on which the State ratified the Inter-American Convention on the Prevention, Punishment, and Eradication of Violence against Women, and 303 Case of Anzualdo Castro v. Peru, supra, para. 65, and Case of Ibsen Cárdenas and Ibsen Peña v. Bolivia, supra, para. 65. 304 Cf. Case of Velásquez Rodríguez v. Honduras. Merits, supra, para. 177, and Case of Contreras v. El Salvador, supra, para. 128. 305 Cf. Case of Anzualdo Castro v. Peru, supra, para. 65, and Case of Contreras v. El Salvador, supra, para. 129. 306 Cf. Case of Velásquez Rodríguez v. Honduras. Merits, supra, para. 181, and Case of Contreras v. El Salvador, supra, para. 129. 80