How to Prosecute Crimes Committed Abroad?

Earlier this year, in U.S. v. Pepe, a former U.S. Marine captain was sentenced to over 200 years in prison for brutally molesting young girls while teaching in Cambodia under the pretense of being a college professor looking out for the Cambodian youth.  He was found guilty of a violation of the PROTECT Act, a laudable federal statute with extraterritorial application which prohibits U.S. citizens from molesting children abroad.  The Pepe case had been lingering for eight years.  The investigation began in 2006, the jury convicted in 2008, and since then the case has been stuck in litigation limbo (a lingering motion for new trial based on an inappropriate relationship between a U.S. law enforcement agent and translator).

I have previously written about the PROTECT Act, and how it, along with numerous other federal statutes that criminalize U.S. citizens behavior abroad, raises an interesting Foreign Commerce Clause (FCC) issue - a matter in which circuit courts are in complete disarray over.  Assuming that Congress, under the FCC, has the power to enact laws like the PROTECT Act with extraterritorial application, the next issues to address (the issues which are framing my fall research project) are the criminal procedure implications of investigations of U.S. citizens in other countries and the related evidentiary matters.

If the U.S. criminally prosecutes a citizen for behavior abroad, when and to what extent should constitutional guarantees (like search and seizure) apply?  It has been suggested that so long as U.S. government agencies train foreign officers, constitutional rights would be secure and the evidence would be admissible.  That seems simplistic, and, indeed, case law is unclear.  For example, under the "joint venture doctrine," a U.S. agency may be so involved with a foreign investigation that the foreign authorities would be deemed as "acting as agents for their American counterparts."  At that point, the U.S. citizen has the right to constitutional protections.  But, the circuits are split as to what level of involvement the U.S. agency has to have to give rise to a joint venture.

What about evidentiary issues?  For example, in one PROTECT Act case, an NGO was helping U.S. and foreign authorities investigate a U.S. citizen traveling in Asia.  When the foreign agents arrested the defendant, an individual from the NGO took the defendant's laptop home which created problematic chain of custody issues at the U.S. trial.  From both practical and legal perspectives, securing witnesses and admissible evidence in the prosecution of extraterritorial crimes create extraordinary legal battles.  Given how easy international travel has become, these issues will become more and more prominent.