In early September 2025, the Genocide Prosecution Network (GPN) published a report on the cumulative prosecution of foreign terrorist fighters (FTFs) for core international crimes and terrorism-related offences, drawing on high-profile jurisprudence in countries such as Germany and the Netherlands. The report aims to equip legal practitioners in the EU and beyond who respond to and prosecute FTFs and female returnees with practical examples and arguments to facilitate their work.

Structured in four main chapters (cumulative charging, evidence, legal defences and judicial assessment, and sentencing), the report:

• Explains the legal and practical implications of cumulative charging (for both terrorism-related offences and core international crimes), including the relevant national and international laws and the cooperation required;
• Details the types of evidence used in cumulative prosecution cases and the overlap between evidence for terrorism and core international crime;
• Sets out the legal defences raised in the context of terrorism-related crimes, compared to those concerning core international crimes;
• Compares sentencing in cumulative prosecution cases with terrorism-only cases, highlighting mitigating and aggravating factors.

The report concludes that cumulatively prosecuting terrorism-related offences alongside core international crimes is essential to ensure comprehensive accountability for FTFs and female returnees, and to deliver justice to victims. This approach effectively addresses the full spectrum of criminal activities committed by ISIS members, ranging from terrorism to core international crimes such as enslavement, sexual violence, and combat-related offences. As the same body of evidence often supports both offence types, the report recommends that national authorities consider both charges from the outset where applicable, question witnesses comprehensively about both, and analyse documentary and forensic evidence through both legal lenses.

Established in 2002, the GPN promotes close cooperation between national authorities investigating and prosecuting genocide, crimes against humanity, and war crimes. Its Secretariat is based at Eurojust.