Subsequent to adoption of the Convention, the International Law Commission studied legal issues relating to its interpretation and implementation in the context of its work on the Code of Crimes against the Peace and Security of Mankind. This included issues such as the nature of participation and the available defences. The Genocide Convention and the crime of genocide are addressed in several international treaties, in particular the International Covenant on Civil and Political Rights, the Convention on the non-applicability of Statutory Limitation, and the Convention on the Suppression and Punishment of Apartheid. The Genocide Convention was also studied in detail by the Sub-Commission on the Prevention of Discrimination and the Protection of Minorities and the Ad Hoc Working Group of Experts on Apartheid. In the 1990s, the crime of genocide as defined in the Convention was incorporated in the statutes of the ad hoc international criminal tribunals for the former Yugoslavia and Rwanda and the International Criminal Court. These courts have all provided judicial interpretation of the definition of genocide taken from the Convention. The Elements of Crimes, adopted pursuant to the Rome Statute of the International Criminal Court, further develop the definition of genocide.