Perhaps you’re a journalist with an unfortunate penchant for referring to the ICC as “the World Court” (sorry, that’s the ICJ) or suggesting that it will hear cases related to decades-ago atrocities (nope, temporal jurisdiction is a thing). Or maybe you’re a student with a term paper to write on how international institutions affect conflict dynamics (nobody knows). Possibly you just wish you could impress your friends with snarky complementarity-themed jokes (which everyone definitely, definitely loves).

If any of these sound like you, the International Center for Transitional Justice has your back. Their new “Handbook on Complementarity” provides, as advertised, a comprehensive (>100 pages!) overview of the role of the ICC and domestic courts in prosecuting atrocity crimes. It’s also a surprisingly good read.

Written by Paul Seils, the Handbook goes ALL IN on the nitty gritty of how complementarity is designed to operate and how the ICC has implemented it so far. Even for relatively well-informed court-watchers, there’s new information. I learned, for instance, that although the prosecutor ordinarily has to wait until the investigation phase to take testimony, in “exceptional cases” where future access to a witness is threatened, she can request authorization from the Pre-Trial Chamber to take testimony during the preliminary examination. Neat! (That’s Rule 47 of the Rules of Procedure and Evidence for those of you following along at home.)

I also discovered that I have been promulgating an inadequate definition of complementarity. (Sorry everyone!) Check it:

In fact, per the Trial Chamber in the Katanga case, the question of whether a case is admissible before the ICC requires a two-stage inquiry: The initial question is whether a national jurisdiction is pursuing the same case as the ICC. It’s only if the answer is yes that the issue of “willing and able” comes up. So I guess we’re all going to have to rewrite our lectures.

A couple of broader themes worth highlighting emerge from this bonanza of information:

1. If you think “is a national jurisdiction pursuing the same case as the ICC” sounds like a simple question, you’re very, very wrong. The meaning of “case” in this context turns out to be a bit of a fraught question, and to have kind of a weird, Heisenberg Uncertainty Principle flavor to it. As a definitional matter, for something to be the same case, it must cover the same suspects, incidents, and conduct. But those elements can remain in flux through several rounds of ICC proceedings. Consequently, a state may be disadvantaged by challenging admissibility before charges are confirmed.
2. One of the effects of the court’s relative youth, along with its resource and jurisdictional constraints, is that anomalous cases can have outsize precedential effect. (And frankly, they’re all pretty anomalous at this point.) With such a limited docket, every ruling provides an important signal about what the court might do in the future. So, for example: “Many people might feel that if the Colombian peace process successfully establishes a justice program with very light sentences that other countries will be able to cite it as a precedent in the future, thus undermining the aims of the ICC.” I am one of these people, and I suspect this is exactly what would happen.

Finally, not that any of us have forgotten, but the Handbook also serves as a useful reminder that prosecuting mass atrocities is HARD. These crimes “often happen on a very large scale and are committed by many different people, in many different places, with many different victims”. Add to that the fact that the passage of time “has a tendency to make legal matters more complicated rather than simpler”, and you have a very complex proceeding on your hands.

And that’s before you bring politics into the mix. For national jurisdictions emerging from conflict or authoritarianism, the legal challenges sit alongside profound political constraints. Prosecuting senior officials or other powerful figures can risk instability or worse. It’s no wonder Seils saw fit to include a 12-step program for national prosecutors investigating serious international crimes. (It’s actually really useful.)

So, in conclusion, thumbs up on the Handbook on Complementarity. Come for the detailed explanation of Article 17, stay for the insightful observations on the necessity of civil society engagement in domestic justice processes and the potentially harmful effects of an uncoordinated influx of donor assistance.

And when you’re done, head on over to the ICTJ’s website and take the Complementarity Quiz. Fun for the whole family!