120. […] Where an error of law is found, it is open to the Appeals Chamber to review the relevant findings of the Trial Chamber according to the correct legal standard.[1] In cases like the instant one, however, where it is submitted that an error of law potentially impacts every single piece of evidence and, by implication, every finding made by the Trial Chamber, the appellate party is required to develop its arguments more precisely by referring to specific portions of the Trial Judgement, thus limiting the import of its allegations – lest the appeal procedure effectively becomes a trial de novo.[2] […]

264. The Trial Chamber considered that “for an accused to be convicted of ‘committing’ pursuant to a theory of [joint criminal enterprise], it must be established that he or she participated in the execution of the common plan or purpose of the enterprise”.[1] The Trial Chamber reasoned that, while Kanyarukiga participated in the planning of the destruction of the Nyange church, there was no evidence to suggest that he ordered, instigated, encouraged, or provided material assistance to the attackers.[2] Accordingly, it concluded that the evidence was insufficient to establish that Kanyarukiga “significantly contributed to the execution or commission of the crimes charged.”[3]

267. The Appeals Chamber notes that the Prosecution does not seek the invalidation of the Trial Judgement, but merely requests clarification on an issue of general importance to the development of the Tribunal’s case law.[4] The Appeals Chamber recalls that the Statute empowers it to hear appeals concerning an alleged error on a question of law “invalidating the decision”.[5] While, in exceptional circumstances, the Appeals Chamber has discretion to hear appeals where a party has raised a legal issue that would not invalidate the judgement,[6] it declines to do so in this case.[7]

35. Errors of law do not raise a question as to the standard of review as directly as errors of fact.  Where a party contends that a Trial Chamber made an error of law, the Appeals Chamber, as the final arbiter of the law of the Tribunal, must determine whether there was such a mistake.  A party alleging that there was an error of law must be prepared to advance arguments in support of the contention; but, if the arguments do not support the contention, that party has not failed to discharge a burden in the sense that a person who fails to discharge a burden automatically loses his point.  The Appeals Chamber may step in and, for other reasons, find in favour of the contention that there is an error of law.

36. Furthermore, this Chamber is only empowered to reverse or revise a decision of the Trial Chamber on the basis of Article 25(1)(a) when there is an error of law that invalidates that decision. It is not any error of law that leads to a reversal or revision of the Trial Chamber’s decision; rather, the appealing party alleging an error of law must also demonstrate that the error renders the decision invalid.

177.    The task of the Appeals Chamber, as defined by Article 24 of the Statute, is to hear appeals from the decisions of Trial Chambers on the grounds of an error on a question of law invalidating the decision or of an error of fact which has occasioned a miscarriage of justice. An appellant must show that the Trial Chamber erred in law or in fact, and the Appeals Chamber expects his arguments to be directed to that end. In the Kambanda Appeal Judgement, the Appeals Chamber was confronted with a similar situation, where the appellant in that case put forward no arguments in support of certain grounds of appeal. The Appeals Chamber found nevertheless that in cases of errors of law it “is not wholly dependent on the arguments of the parties.” In such cases it found that it retained the discretion “in proper cases to consider an issue raised on appeal even in the absence of substantial argument.” […]

See also para. 344.

65. […] [C]onsidering that “time served” is not among the penalties provided in the Statute and the Rules that may be imposed on a person found guilty of contempt, the Appeals Chamber finds that, by sentencing Fatuma to “time served”, the Single Judge did not impose a permissible sentence. It was incumbent on the Single Judge, when electing to impose a sentence of imprisonment, to first determine the term of imprisonment and then, in accordance with Rule 125(C) of the Rules, give credit for the time that Fatuma had spent in detention in the custody of the Mechanism pending trial. Accordingly, the Appeals Chamber finds, proprio motu, that by not determining a specific term of imprisonment, the Single Judge committed an error in failing to follow the applicable law. […]