Chicago Journal of International Law Pursuant to Article 25(3)(c), aiding and abetting consists of two elements, the actus reus and the mens rea.119 The ICC construes the actus reus of aiding and abetting to be the provision of practical or material as well as moral or psychological assistance to the principal perpetrator.120 However, the “precise actus reus threshold” remains an open question.121 The tribunals may provide useful insight to this effect. They have held that “aiding and abetting requires acts or omissions that assist, encourage or lend moral support to crimes.”122 The tribunals have also required that the aider and abettor’s conduct “substantially” contribute to the commission, similar to the ICC’s notion of “material” assistance.123 The mens rea for aiding and abetting under the Rome Statute, as indicated in Article 25(3)(c), is purpose.124 This requirement is markedly harder to prove than the mens rea applied by ad hoc tribunals, which is knowledge.125 For example, the ICTY Trial Chamber in Šešelj held that, as it pertains to the defendant’s contributions, “the aider and abettor must have known that these acts had contributed to the perpetration of the crime and been aware of the essential elements of the crime, including the intent of the principal perpetrator, without necessarily knowing the exact crime that was intended or committed.”126 Although the Rome Statute’s mens rea for aiding and abetting is higher than the standard applied by the ad hoc tribunals, common purpose liability—a Rome Statute innovation—effectively lowers it back to knowledge for group crimes. B. Common Purpose Article 25(3)(d) of the Rome Statute establishes “common purpose liability,” which this Comment considers a form of complicity. The Article stipulates: In accordance with this Statute, a person shall be criminally responsible and liable for punishment for a crime within the jurisdiction of the Court if that person . . . in any other way contributes to the commission or attempted commission of such a crime by a group of persons acting with a common purpose. Such contribution shall be intentional and shall either: 119 120 121 122 123 124 125 126 Cassel, supra note 116, at 308. Manuel J. Ventura, Aiding and Abetting, in MODES OF LIABILITY IN INTERNATIONAL CRIMINAL LAW 173, 176 (Jérôme de Hemptinne et al. eds., 2019). Id. at 177. Id. at 176. Id. at 177. Id. at 178. Id. Prosecutor v. Šešelj, Case No. IT-03-67, Judgment, ¶ 353 (Int’l Crim. Trib. for the Former Yugoslavia Mar. 31, 2016), http://perma.cc/HP8B-NQZR. 100 Vol. 21 No. 1