...a handful of legal cases in the US are beginning to define the legal boundaries under which [private military] companies can operate...Although they differ in their specifics, the cases are "all about figuring out the limits of accountability in the absence of any regulation", said Peter Singer, an expert on private military companies at the Brookings Institution in Washington...Civilian contractors are not subject to military justice and are almost never tried at home for acts committed abroad. The conflict zones in which they operate rarely have a functioning justice system that could try them, either. [refers to Blackwater, California Microwave (part of Northrop Grumman), CACI, Titan]