In my course on transitional justice, we start with the International Military Tribunal (aka Nuremberg Trial) and the impossibility of bringing all perpetrators to justice in the wake of mass atrocities and large-scale human rights abuses.
The legal system doesn’t have the resources to investigate, identify, charge, and bring to justice every single individual who participated in and facilitated the violence. So you start with “big fish.” The architects and instigators. Who gave the orders?