How can national courts use universal jurisdiction to prosecute war crimes?

Under international law, national courts can use universal jurisdiction to prosecute war crimes, genocide, and crimes against humanity regardless of where the crimes occurred or the nationality of the offenders or victims. This principle allows states to bypass traditional jurisdictional limits—which typically restrict courts to crimes committed within their territory or by their own nationals—to ensure that grave offenses do not go unpunished.12

The application of universal jurisdiction often functions through the following mechanisms:

• Duty to Prosecute or Extradite: For grave breaches of the Geneva Conventions and acts of torture, international treaties establish the principle of aut dedere aut judicare ("either adjudicate or extradite"). This mandates that national governments must either try the offenders themselves or extradite them to a country prepared to do so.2
• Legislative Implementation: States may enact domestic legislation to incorporate these international obligations. For example, the United Kingdom’s Geneva Conventions Act of 1957 made it a criminal offense for any person to commit a grave breach of the conventions anywhere in the world.3
• Custody Requirements: Courts generally require custody of the defendant to proceed with a trial, as demonstrated in the case of Attorney General of the Government of Israel v. Eichmann, where the court held that such acts could be tried by any state that had custody of the accused.3

It is a fundamental ethical principle that those who commit atrocities against humanity must be held accountable, and universal jurisdiction serves as a critical legal tool to prevent impunity for such heinous acts.23