[Update - I've clarified some points below, at the bottom, in response to reader feedback]
Ben Emmerson QC is a British human rights law specialist who currently serves as the UN Human Rights Council's "Special Rapporteur on Counter-Terrorism and Human Rights" (this poisition is one of several dozen thematic or country-specific investigative entities set up by the HRC under its "special procedures" system). Last summer he appeared at a conference organized by the ACLU in Geneva. Participants in the event, including his fellow special rapporteur Christof Heyns (SR for Extrajudicial Killings, etc.), harshly criticized U.S. policies, and Emerson followed suit (see here for an overview). Here's some of what he had to say at that time:
Emmerson said that protection of the right to life required countries to establish independent inquiries into each drone killing. "That needs to be applied in the context of targeted killings," he said. "It's possible for a state to establish an independent ombudsman to inquire into every attack and there needs to be a report to justify [the killing]."
Alternatively, he said, it was "for the UN itself to consider establishing an investigatory body. Drones attacks by the US raise fundamental questions which are a direct consequence of my mandate… If they don't [investigate] themselves, we will do it for them."
It is time, he added, to end the "conspiracy of silence" over drone attacks and "shine the light of independent investigation" into the process. The attacks, he noted, were not only on those who had been killed but on the system of "international law itself".
A few months later, Emerson returned to the illegality theme, this time in a speech at Harvard:
‘The [global] war paradigm was always based on the flimsiest of reasoning, and was not supported even by close allies of the US,’ he added. ’The first-term Obama administration initially retreated from this approach, but over the past 18 months it has begun to rear its head once again, in briefings by administration officials seeking to provide a legal justification for the drone programme of targeted killing in Pakistan, Yemen and Somalia.’
Well, Emerson has now launched his formal investigation. Here is his statement explaining its purpose, scope, and procedures. It emphasizes that there is sharp debate regarding which legal regimes apply to targeted strikes in various contexts, and then goes on to indicate that Emerson will focus on questions of proportionality, post-strike investigation, and post-investigation remediation:
The central objective of the present investigation is to look at the evidence that drone strikes and other forms of remote targeted killing have caused disproportionate civilian casualties in some instances, and to make recommendations concerning the duty of States to conduct thorough independent and impartial investigations into such allegations, with a view to securing accountability and reparation where things can be shown to have gone badly wrong with potentially grave consequences for civilians.
So this is where it gets interesting: Whether there actually is a legal obligation applicable to the United States that requires post-strike investigation into allegations of a proportionality violation; whether, if so, that obligation is properly described as requiring the investigation to be "independent"; and just what suffices as "independent" in that case. It will be very interesting to see whether the report squarely and fairly wrestles with these questions. It must do so if it is to have any chance of making a splash among folks not already convinced of the illegality of targeted strikes; a paragraph or two referencing ECHR caselaw and HRC interpretive statements will not do the trick.
[UPDATE: Some careful readers point out that I was not a careful writer in this paragraph, so let me elaborate a bit more. The first question I pose above is whether there is an applicable investigation rule. What I mainly have in mind here is the dispute over whether IHRL rules govern, whether IHL rules govern, or both in some fashion (or of course the answer could differ from context to context). I did not mean to suggest IHRL contains no rule of this kind, nor that there are no circumstances in which IHL could be said to require something along these lines; I just mean to flag that there is a need here to come to grips with the dispute over which legal regime(s) is(are) applicable. But let's not get too focused on that part, for I tend to agree with some of those who wrote me who contended that the key question is what legal obligation can be established with respect to which circumstances require investigation and what precisely "independence" would mean here. As to the former, if there is an investigation obligation, does it attach across the board to all uses of force in the circumstances here in issue, or just some (consider, in this regard, pp. 432-33 of Melzer's Targeted Killing in International Law, which distinguishes between the impact of an investigative obligation where the person killed was "of undisputed (functional or privileged) combatant status and where instead you have a DPH scenario). And as to the latter, is it enough to simply have different personnel from the same investigation conduct the review? Must they be outside the same chain-of-command in a narrow sense? From a separate organization altogether? Must it be judicial? And as a meta-issue overlaying these, is it obligatory in a legal sense for the US government to show in public the details of just what sort of post-strike accounting it does engage in? These are the issues I hope will be addressed in a detailed way in Emerson's report.]