This post is the latest installment of our “Monday Reflections” feature, in which a different Just Security editor examines the big stories from the previous week or looks ahead to key developments on the horizon.

Pre-trial proceedings were again underway last week before the military commission trying the case involving the 9/11 defendants, United States v. Khalid Shaikh Mohammad et al. (KSM). (The indomitable Carol Rosenberg tweeted continuous coverage.) I’d like to re-alert readers to one of the core legal issues in the case that may be getting lost in the shuffle given all the noise surrounding those proceedings (including controversy over a ban on female guards touching the defendants based upon an argument that any such physical contact violates the defendants’ Muslim beliefs because the guards, being non-mahram (unrelated), are eligible for marriage).

On these pages and elsewhere, I have covered a doctrinal debate playing out in several legal fora — including international tribunals and U.S. federal courts hearing Alien Tort Statute cases — over the correct mens rea and actus reus standards for proving complicity liability. (You can find a few other posts on this here and here.) These issues have also arisen in the KSM case.

Our readers will recall that the Chief Prosecutor, Brig. Gen. Mark Martins, tried to withdraw Charge 1 of the original charge sheet — inchoate conspiracy as a standalone offense — in order to focus on “legally sustainable charges.” The then-Convening Authority, Vice Adm. Bruce MacDonald, tried to block this move, ostensibly because the Justice Department was vigorously defending the charge in another case, United States v. al Bahlul, as others on these pages have discussed. In the end, the prosecutor, in a brief filed in January 2013, simply failed to oppose the defense motion to dismiss the charge, a decision over which the Convening Authority had no control.

The prosecutor subsequently filed a brief seeking to make certain “minor conforming changes to the charge sheet.” Specifically, the prosecutor sought to amend the charge sheet to retain certain allegations that had been associated with Charge 1. The prosecutor made clear that he intended to go forward with the full range of theories of liability — including aiding and abetting, joint criminal enterprise, conspiracy, and common purpose — in connection with the remaining substantive charges, including the war crimes of attacking civilians, murder, and related offenses. (See here for a list of prosecutable forms of responsibility before the military commissions.) In particular, the brief noted: 

At trial, the government intends to prove an agreement between the five Accused and others, as well as overt acts committed by each Accused, that will establish each of their criminal liability as principals for aiding, abetting, counseling, commanding, or conspiring to commit the substantive law of war offenses that were committed during the September 11, 2001 attacks that killed 2,976 people.

The brief sought to reformulate the relevant passages of the original charge sheet as “common allegations” to “establish how each Accused is alleged to have aided, abetted, counseled, commanded, or conspired to commit the attacks [and] to keep the accused on notice of all theories liability and to reduce confusion for the panel members.”

The prosecutor brought to the commission’s attention the then-recent decision in the case against Charles Taylor before the Special Court for Sierra Leone (SCSL), citing it for its customary international law analysis of accomplice liability. The U.S. government brief cited with approval several important holdings of the SCSL of relevance to ongoing debates about the scope of complicity liability and, in so doing, set forth the U.S. government’s view on the correct legal standards. In particular, the brief adopts the following holdings by the SCSL:

To satisfy the actus reus of aiding and abetting liability it must be shown that

  • The accused provided practical assistance, encouragement, or moral support to the perpetration of a crime or underlying offense, and
  • Such practical assistance, encouragement, or moral support had a substantial effect upon the commission of a crime or underlying offense (paras. 353, 362).


  • The assistance need not be directly provided to the actual criminal perpetrator, nor must it be used in the commission of a specific crime (paras. 368, 371).
  • Though the total effect on the commission of a crime is a factual determination, a “but for” causation standard is not required, nor must the assistance be specifically directed towards a crime (paras. 353, 390-392, 476-480).

The mens rea for accomplice liability is proven with a showing that

  • The accused performed an act with the knowledge that such act would assist the commission of a crime or underlying offense, or that he was aware of the substantial likelihood that his acts would assist the commission of an underlying offense, and
  • The accused is aware of the essential elements of the crime committed by the principal offender, including the state of mind of the principal offender (paras. 403, 436-437).

As a result,

  • The knowledge required is simply a knowing participation that the acts would assist the commission of a crime. A conscious desire or willingness to achieve the criminal result is not required (paras. 436-437).

The government’s brief thus follows two International Criminal Tribunal for the former Yugoslavia (ICTY) Appeals Chambers (Prosecutor v. Sainović and Prosecutor v. Popović) and the SCSL in rejecting the “specific direction” approach to actus reus advanced by one ICTY Appeals Chamber in Prosecutor v. Perišić. Moreover, the government also makes clear that it is the knowledge standard for mens rea that must be met to secure a conviction before the military commissions. To be sure, if the alleged acts of assistance are proven at trial, the 9/11 accused would easily satisfy the higher “purpose” standard advocated by some ATS defendants, but this will not be the operative standard if the military commissions adopt the U.S. government’s reasoning.