A recent and prominent American appeals court case has revived a controversial international law question: can a state compel a person on its territory to obtain and produce material that the person owns or controls, but which is stored on the territory of a foreign state? The case involved, United States v Microsoft, features electronic data stored offshore that was sought in the context of a criminal prosecution. It highlights the current legal complexity surrounding the cross-border gathering of electronic evidence, which has produced friction and divergent state practice. The author here contends that the problems involved are best understood — and potentially resolved — via an examination through the lens of the public international law of jurisdiction and, specifically, the prohibition of extraterritorial enforcement jurisdiction. An analysis of state practice reveals that unsanctioned cross-border evidence gathering is viewed by states as an intrusion on territorial sovereignty, engaging the prohibition, and that this view properly extends to the kind of state activity dealt with in the Microsoft Ireland case.
