" Imagine the killing of 100,000 people who happened to come from the same group,” I explained, “Jews or Poles in the city of Lviv. For Lauterpacht, the killing of individuals, if part of a systematic plan, would be a crime against humanity. For Lemkin, the focus was genocide, the killing of the many with the intention of destroying the group of which they were a part. For a prosecutor today, the difference between the two was largely the question of establishing intent: to prove genocide, you needed to show that the act of killing was motivated by an intent to destroy the group, whereas for crimes against humanity no such intent had to be shown.” I explained that proving intent to destroy a group in whole or in part was notoriously difficult, since those involved in such killings tended not to leave a trail of helpful paperwork. "

― Philippe Sands , East West Street: On the Origins of "Genocide" and "Crimes Against Humanity"