[The Court entered into the question of immunities of the Minister of Foreign Affairs on the assumption that the Belgian judge had jurisdiction to issue the arrest warrant]
52. The Vienna Convention on Diplomatic Relations of 18 April 1961… states in its preamble that the purpose of diplomatic privileges and immunities is to ‘ensure the efficient performance of the functions of diplomatic missions as representing States’ … only the sending State may waive such immunity… on these point the Vienna Convention … reflects customary international law
53. In customary international law, the immunities accorded to Ministers of Foreign Affairs are not granted for their personal benefit, but to ensure the effective performance of their functions on behalf of their respective States.
54. The Court accordingly concludes that the functions of a Minister of Foreign Affairs are such that, throughout the duration of his or her office, he or she when abroad enjoys full immunity from criminal jurisdiction and inviolability.
55. In this respect, no distinction can be drawn between acts performed … in an ‘official’ capacity, and those … in a ‘private capacity’, or, for that matter, between acts performed before the person concerned assumed office as Minister of Foreign Affairs and acts committed during the period of office
[The Court turned to the argument that immunities cannot protect in cases of war crimes or crimes against humanity]
58. The Court has carefully examined State practice… It has been unable to deduce … that there exist under customary international law any form of exception to the rule according immunity from criminal jurisdiction and inviolability to incumbent Ministers of Foreign Affairs, when they are suspected of having committed war crimes or crimes against humanity
59. … Rules governing the jurisdiction of national courts must be carefully distinguished from those governing jurisdiction immunities: jurisdiction does not imply absence of immunity, while absence of immunity does not imply jurisdiction. Thus although various international conventions … impose on States obligations of prosecutions or extradition, thereby requiring them to extend their criminal jurisdiction, such extension of jurisdiction in no way affects immunities under customary international law.
60. The Court emphasizes, however, that the immunity from jurisdiction … does not mean … impunity … Immunity from criminal jurisdiction and individual criminal responsibility are quite separate concepts. While jurisdictional immunity is procedural in nature, criminal responsibility is a question of substantive law. Jurisdictional immunity may well bar prosecution for a certain period or for certain offences; it cannot exonerate the person to whom it applies from all criminal responsibility.
61. …Immunities… do not represent a bar to criminal prosecution in certain cases… after a person ceases to hold the office… he or she will no longer enjoy all of the immunities accorded by international law … A court of a State may try a former Minister of Foreign Affairs of another State in respect of acts committed prior or subsequent to his or her period of office, as well as in respect of acts committed during that period or office in a private capacity … An incumbent of former Minister of Foreign Affairs may be subject to criminal proceedings before certain international criminal courts where they have jurisdiction