This article explores the problem of attribution in the context of R2P intervention through an analysis of the Syrian chemical weapons attack of 2013. We argue that R2P advocates can be confronted by a crisis dynamic where the political momentum for military intervention runs ahead of independent verification and attribution of mass atrocity crimes. We contrast the political momentum for intervention with the technical process of independent attribution and show that the sort of independent evidence that would ideally legitimize an R2P intervention was unavailable when there was political momentum for action. Conversely, the information that was available (which inevitably informed the political momentum for action) was largely produced by state intelligence organisations – or a potentially briefed media – and shaped by the interests and priorities of its end users. While understandable in the face of the ‘extreme’, we suggest that the mobilisation of political momentum by R2P advocates entails significant dangers: first, it risks undermining the integrity of R2P if evidence is later discredited; and, second, it risks amplifying the perception that states sometimes exploit humanitarian pretexts in pursuit of other strategic ends.