As of March 2013 out of 192 UN member states, 122 are States Parties to the Rome Statute of the International Criminal Court (ICC).
States which have ratified or acceded to the ICC Statute are known as State Parties. They are under an obligation to implement the provisions of the Statute in their domestic law. In particular, the state has to criminalise genocide, crimes against humanity and war crimes in its national legislation. These crimes are specifically defined in the ICC Statute under Articles 6, 7 and 8, respectively.
ICC’s jurisdiction is complementary to national jurisdiction
The ICC is not intended to be a substitute for national criminal justice systems. It complements them. This is known as the principle of complementarity (see Article 17 of the ICC Statute). According to it the ICC does not have jurisdiction if the state is investigating or prosecuting, unless the state is unwilling or unable to do so genuinely. The same applies where a state has investigated and decided not to prosecute. The ICC would not have jurisdiction unless the decision not to prosecute resulted from unwillingness or inability genuinely to prosecute.
The implication of this is that if a state has not even investigated, say, crimes against humanity committed on its own territory or by its nationals, the ICC does have jurisdiction.
However, it would be unrealistic to expect that the ICC will be able to try all such crimes and punish all perpetrators. As a matter of practicality the ICC cannot be the first instance court for such crimes.
To satisfy the definition of crimes against humanity, for example, such crimes have to be committed as part of a widespread or systematic attack directed against a civilian population. Such crimes typically have numerous perpetrators. Consider allegations of killings and torture inflicted in camps, spread across a war-torn country over the course of several years. One cannot realistically expect all the perpetrators to find themselves before the ICC. The effectiveness of the whole system, therefore, depends on national prosecutions of these crimes.
The integrity of the ICC model rests on the premise that State Parties will act to prosecute genocide, crimes against humanity and war crimes committed on their territory or by their nationals. The assumption is that the ICC would exercise its complementary jurisdiction in the minority of cases where false national prosecutions attempt to shield someone from ICC prosecution, or states are unable to prosecute because their national judicial system has collapsed.
As reiterated in the Complementarity Resolution by the Assembly of State Parties adopted at the ICC Review Conference in Kampala in 2010, effective prosecution of the core international crimes must be ensured at the national level. Around one half of States Parties have some type of implementing legislation. The Peace and Justice initiative can assist States Parties and other states in drafting and reviewing implementing legislation and training relevant stakeholders in using those provisions in practice in domestic trials.