The Second Circuit has just handed down a very important new Fourth Amendment case on how the Fourth Amendment applies overseas: In re Terrorist Bombings of U.S. Embassies (Fourth Amendment Challenges). In an opinion by Judge Cabranes, the court held that the warrant requirement does not apply to searches abroad conducted by U.S. officials: searches abroad are governed by a reasonableness standard instead of the warrant requirement.

  It's interesting to compare the Second Circuit's approach with the rule that the Ninth Circuit has taken in cases involving joint investigations. In most criminal cases investigated abroad, the U.S. works closely with foreign law enforcement: the FBI and the foreign authorities conduct a joint investigation. In that setting, the Ninth Circuit has held that the Fourth Amendment requires reasonableness, and that the reasonableness of a joint investigation is governed by its compliance with the law where the search occurred. The basic idea is that if the U.S. law enforcement authorities are working with their foreign counterparts and conducting searches abroad, then the most you can expect is that the joint investigation will comply with the letter of the law where the search is occurring.

  Today's decision by the Second Circuit deals with a different circumstance: Here the U.S. was acting alone, with intelligence agencies investigating in Kenya without the assistance of Kenyan authorities. Until today, there were no federal appellate decisions on this set of facts, and the only lower court decision (that I know of) was the district court decision below. The Second Circuit applied a different sort of reasonableness rule: It applied a totality of the circumstances test that generally balances the individual's privacy interest with the government's interest in collecting the information. Notably, in this case the test factored in the government's national security interests in investigating terrorism -- an interest that the court indicated was paramount and that the court was "loathe" to discount.

  This is roughly the framework that it seems that U.S. intelligence agencies had been assuming applying to its surveillance of those with Fourth Amendment rights abroad, and if anything is more government-friendly than the very sparse precedents in this area would suggest -- certainly more so than Judge Sand's opinion for the district court. But this area has long been a question mark in the Fourth Amendment area: While there have been a number of "joint investigation" cases, the legal framework for U.S.-only monitoring of U.S. citizens abroad has long been a largely open question.

  Finally, note that this opinion doesn't change the law that applies to the bulk of national security monitoring abroad. Most national security surveillance outside the U.S. is of individuals that have no Fourth Amendment rights at all under United States v Verdugo-Urquidez because they have no significant voluntary contact with the U.S. (such as would generally be the case with a foreigner abroad who doesn't live in the U.S. or have property here). The rules that apply to such monitoring is statutory rather than constitutional, and this decision (which applies in the case of a U.S. citizen) doesn't change that.