This paper addresses the intersection between two key concepts in
international criminal justice, namely cooperation and complementarity.
While it is recognised that domestic courts carry main responsibility for
ensuring accountability for the commission of international crimes, there
appears to be gaps in two areas. First, international law does not make
provision for a comprehensive obligation to investigate and prosecute
such crimes. Second, there is no comprehensive and robust interstate
cooperation obligation, necessary to ensure successful
domestic investigations and prosecutions. The paper assess two
initiatives designed to fill these gaps, and considers their strengths,
weaknesses and the possible synergies between them.