The present paper addresses the fall of Baghdad and examines some accusations made against Khwāja Nasīr al-Dīn Tūsī. This issue is specified in an statistical-analytic study of valid historical sources and in response to Ibn Taymiya’s accusations, two notions are brought up: one is whether Khwāja Nasīr is one of the most important Ismā‘īlī figures and among their counselors and viziers; and the other is whether he issued the order for the murder of the Abbasid caliph.