A/HRC/19/57 determining the extent of international law obligations that may have a direct or indirect effect on matters before them, the reports and Opinions of the Working Group have provided assistance. This also applies when a national court considers a detention that the Working Group has declared arbitrary in violation of international law. The effectiveness of international human rights protection requires that all national authorities observe international law obligations. The Working Group has on occasion reminded a State that the duty to comply with international human rights rests not only on the Government but on all officials, including judges, police and security officers, and prison officers with relevant responsibilities. No person can contribute to human rights violations. The Working Group has also made clear that a widespread or systematic practice of detention can constitute a war crime or a crime against humanity. 68. The Working Group has in its jurisprudence established the ways in which it deals with evidentiary issues. Its approach is in line with the ruling of the International Court of Justice in Ahmadou Sadio Diallo (Republic of Guinea v. Democratic Republic of the Congo), which establishes the evidentiary position for claims to succeed in human rights cases, a position which this Working Group has adopted on previous occasions for its own Opinions in individual cases. Where it is alleged that a person has not been afforded, by a public authority, certain procedural guarantees to which he or she was entitled, it may be difficult to establish the negative fact that is asserted. A public authority is generally able to demonstrate that it has followed the appropriate procedures and applied the guarantees required by law – if such was the case – by producing documentary evidence of the actions that were carried out. In general the burden rests with the Government: it is for the Government to produce the necessary proof. More generally, the matter of the evidentiary burden arises where the source has established a prima facie case for breach of international requirements constituting arbitrary detention. Regrettably, in some cases, Governments have not responded to the request from the Working Group to provide it with information. In the absence of such information, the Working Group must base its Opinion on the prima facie case as made out by the source. Furthermore, mere assertions that lawful procedures have been followed will not be sufficient to rebut the source’s allegations; that follows from the nature of the prohibition of arbitrary detention. 69. The Working Group promotes compliance with international human rights law and standards prohibiting and preventing arbitrary detention, as expressed in the Universal Declaration of Human Rights and the International Covenant on Civil and Political Rights. The Human Rights Committee has authoritatively confirmed that “arbitrary deprivations of liberty” constitute a violation of peremptory norms of international law which are nonderogable (see general comment No. 29 (2001) on derogation during a state of emergency). In agreement with this position, the Working Group continues to apply the prohibition of arbitrary detention as a peremptory norm of international law (or jus cogens). The Working Group is preparing a deliberation on arbitrary detention in customary international law, which, among other matters, will provide an overview of statements by other bodies and the Working Group’s own practice on what constitutes detention, the legality requirement and the prohibition of arbitrariness, in pre- and post-trial detention and detention during the trial, including the principles of necessity and proportionality which are at the core of the arbitrariness requirement. 70. In addition to promoting compliance with international human rights law and standards prohibiting and preventing arbitrary detention, the Working Group continues to promote adequate redress when arbitrary detention has occurred, in terms of articles 2, paragraph 3, and 9, paragraphs 4 and 5, of the International Covenant on Civil and Political Rights and the requirements of customary international law. Having established the arbitrariness of detention in its Opinion, the Working Group will request the Government to take the necessary steps to remedy the situation and to bring it into conformity with the standards and principles of the Universal Declaration of Human Rights and the Covenant. 22