65. It follows from the terms of the two provisions cited above that the expulsion of an alien lawfully in the territory of a State which is a party to these instruments can only be compatible with the international obligations of that State if it is decided in accordance with “the law”, in other words the domestic law applicable in that respect. Compliance with international law is to some extent dependent here on compliance with internal law. However, it is clear that while “accordance with law” as thus defined is a necessary condition for compliance with the above-mentioned provisions, it is not the sufficient condition. First, the applicable domestic law must itself be compatible with the other requirements of the Covenant and the African Charter; second, an expulsion must not be arbitrary in nature, since protection against arbitrary treatment lies at the heart of the rights guaranteed by the international norms protecting human rights, in particular those set out in the two treaties applicable in this case.
72. However, the Court is of the opinion that this decree did not comply with the provisions of Congolese law for two other reasons.
First, it was not preceded by consultation of the National Immigration Board, whose opinion is required by Article 16 of the above-mentioned Legislative Order concerning immigration control before any expulsion measure is taken against an alien holding a residence permit… Second, the expulsion decree should have been “reasoned” pursuant to Article 15 of the 1983 Legislative Order; in other words, it should have indicated the grounds for the decision taken. The fact is that the general, stereotyped reasoning included in the decree cannot in any way be regarded as meeting the requirements of the legislation. The decree confines itself to stating that the “presence and conduct [of Mr. Diallo] have breached Zairean public order, especially in the economic, financial and monetary areas, and continue to do so”. The first part of this sentence simply paraphrases the legal basis for any expulsion measure according to Congolese law, since Article 15 of the 1983 Legislative Order permits the expulsion of any alien “who, by his presence or conduct, breaches or threatens to breach the peace or public order”. As for the second part, while it represents an addition, this is so vague that it is impossible to know on the basis of which
activities the presence of Mr. Diallo was deemed to be a threat to public order (in the same sense, mutatis mutandis, see Certain Questions of Mutual Assistance in Criminal Matters (Djibouti v.
France), Judgment, I.C.J. Reports 2008, p. 231, para. 152).
73. The Court thus concludes that in two important respects, concerning procedural guarantees conferred on aliens by Congolese law and aimed at protecting the persons in question against the risk of arbitrary treatment, the expulsion of Mr. Diallo was not decided “in accordance with law”.
Consequently, regardless of whether that expulsion was justified on the merits, a question to which the Court will return later in this Judgment, the disputed measure violated Article 13 of the Covenant and Article 12, paragraph 4, of the African Charter.
75. Article 9, paragraphs 1 and 2, of the Covenant provides that:
“1. Everyone has the right to liberty and security of person. No one shall be subjected to arbitrary arrest or detention. No one shall be deprived of his liberty except on such grounds and in accordance with such procedure as are established by law.
Article 6 of the African Charter provides that:
“Every individual shall have the right to liberty and to the security of his person. No one may be deprived of his freedom except for reasons and conditions previously laid down by law. In particular, no one may be arbitrarily arrested or detained.”
82….it is difficult not to discern a link between Mr. Diallo’s expulsion and the fact that he had attempted to recover debts which he believed were owed to his companies by, amongst others, the Zairean State or companies in which the State holds a substantial portion of the capital, bringing cases for this purpose before the civil courts. Under these circumstances, the arrest and detention aimed at allowing such an expulsion measure, one without any defensible
basis, to be effected can only be characterized as arbitrary within the meaning of Article 9, paragraph 1, of the Covenant and Article 6 of the African Charter.