Pinpointing responsibility for mass atrocities on particular individuals – as the criminal law demands – is an elusive and perilous enterprise. Genocide, war crimes, and crimes against humanity occur in the havoc of civil strife, in teeming prison camps, and in the muck and messiness of heated combat. The victims are either dead or, if willing to testify, “unlikely to have been taking contemporaneous notes.” There are the anonymity of mass graves, the gaps and uncertainties in forensic evidence, the complexity of long testimony covering several places and periods, years ago. There is also the fluidity of influence by leaders over followers and of equals in rank over one another, as well as the uncertain measure of freedom from others – both superiors and peers – enjoyed by all. The central questions become:

1. How does mass atrocity happen?

2. How should criminal law respond?

The two queries are generally asked in isolation: the first by social scientists and historians, the second by courts and lawyers. Properly understood, the questions are inseparable, this book shows, for the law stands to learn much from careful attention to atrocity's actual dynamics. The law itself permits the trial of hundreds or even thousands, each for any number of serious offenses (as is often the case). Prosecutors hence confess that they enjoy great discretion over how to proceed. This freedom should surely be exercised in light of the best understandings of how and why mass atrocity occurred.