In comparison, immunity derives from the position held by the person in question. There are two types of immunities under common international law: ratione materiae (functional) and ratione personae (personal).
Functional immunity protects certain senior officials (chiefs of state, prime ministers, foreign ministers, etc…) from prosecution in other countries for acts committed within the context of their official duties. This immunity is justified under customary international law by the fact that the actions of such persons are imputed to the state (cf. Blaškić, Decision of the Appeals Chamber of the ICTY 29 Oct. 2007, § 38). Functional immunity are linked to a position rather than a specific person. What is more, this immunity is permanent, which means that an official who has this protection can never be brought to justice even after she has left her post. For example, in November 2007, a French prosecutor refused to indict the former United States Secretary of Defense, Donald Rumsfeld for crimes allegedly committed during the 2003 invasion of Iraq because he was still protected by functional immunity.
However, a person benefiting from functional immunity may be brought before a court for acts committed in her personal capacity. For example, an official accused of having stolen funds would not be protected by functional immunity because her acts were outside of her official duties and cannot be attributed to the state.
It is now generally recognized that immunity does not protect state actors from prosecution in international courts for the most serious international crimes (war crimes, crimes against humanity, torture and genocide). This is because such acts can never be considered as part of a state’s legitimate function so that they may not be imputed to it. This defense has been disavowed by the Nuremberg Charter (article 7), the Genocide Convention (article 4), the Statute of the International Criminal Tribunal for the former Yugoslavia (article 7(2)), the Statute of the International Criminal Tribunal for Rwanda (article 6(2)) and the Rome Statute of the International Criminal Court (article 27).
Other courts have also refused to recognize functional immunity. In May 2004, the Special Court for Sierra Leone held that sovereign equality did not preclude the prosecution of a sitting head of state by an international tribunal and indicted Charles Taylor. In March 2009, the International Criminal Court also found that functional immunity was not an impenetrable defense when it indicted Sudanese president Omar Al-Bashir. This was the first arrest warrant issued against a sitting head of state.
In one of the most famous decisions cited in favor of a limited application of functional immunity, the House of Lords held on November 25, 1998 that Augusto Pinochet, former president of Chile, could not benefit from functional immunity for “international crimes” (known as jus cogens or crimes giving rise to universal jurisdiction) such as torture or hostage taking (Pinochet I Judgment).
However, functional immunity is still an important protection under domestic law. The International Court of Justice reaffirmed this in the Case Concerning the Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v. Belgium). In its decision, the Court struck the arrest warrant issued against Abdulaye Yerodia Ndombasi, then the Minister for Foreign Affairs of the DRC, by Belgium authorities affirming that he benefited from functional immunity and could only be prosecuted for personal acts committed while in office.
In contrast, personal immunity is absolute, individual and temporary. This form of immunity protects certain senior officials (heads of State, diplomatic agents, ministers of foreign affairs, etc.) from all law suits while they are in office. This immunity is justified on the basis that such officials and diplomats require a certain amount of independence to be able to effectively exercise their functions.
In June 2002, the International Court of Justice affirmed that absolute immunity of the DRC’s Minister for Foreign Affairs in the Case Concerning the Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v. Belgium). The Court held that an arrest warrant could not be issued against a sitting minister of foreign affairs because he had to be able to travel freely in order to fulfill his mission. Contrasting this decision with the Pinochet case highlights the difference between functional and personal immunity. Even though functional immunity cannot be invoked in an international court in the case of the most serious international crimes, Yerodia was protected by his personal immunity as long as he exercised the function of minister of foreign affairs.
Domestic courts have also largely affirmed the absolute right to personal immunity (complaints have been rejected against Fidel Castro in Belgium and Spain because he benefited from personal immunity as a sitting head of state, complaints against Colonel Kadhafi and Ariel Sharon were also rejected for the same reason in French and Belgian courts, respectively).
However, international criminal courts have not always recognized personal immunities. For example, Slobodan Milošević was indicted by the International Criminal Tribunal for the former Yugoslavia (ICTY) while he was still president of the Federal Republic of Yugoslavia and the trial of Charles Taylor began before the Special Court for Sierra Leone while he was sitting president of Liberia. Finally, the International Criminal Court issued an arrest warrant against the head of Soudan, Omar Al-Bashir during his presidency.