On 24 April 1915, Talaat issued an to close all Armenian political organizations operating within the Ottoman Empire and arrest Armenians connected to them, justifying the action by stating that the organizations were controlled from outside the empire, were inciting upheavals behind the Ottoman lines, and were cooperating with Russian forces. This order resulted in the arrest on the night of 24–25 April 1915 of 235 to 270 Armenian community leaders in Constantinople, including politicians, clergymen, physicians, authors, journalists, lawyers, and teachers, the majority of whom were eventually murdered, including his colleagues Zohrab and Serengülian. Although the mass killings of Armenian civilians had begun in the vilayet of Van several weeks earlier, these mass arrests in Constantinople are considered by many commentators to be the start of the Armenian genocide.