 Complete the following phrase:  In 1868, he was appointed to the Imperial Council of State in Istanbul. In 1872, he wrote a memorandum to the Grand Vizier, Mahmud Nedim Pasha, exposing the existence of a secret Bulgarian revolutionary society and its possible ties to Serbia. From then until 1873, he served on a three-member government commission investigating the , involving the theft of tax revenues from the Royal Treasury, and the activities of the Bulgarian Revolutionary Central Committee. The commission would sentence one of its leaders, Vasil Levski, to death; an act for which he has sometimes been denounced as a traitor. In 1876, he served on another commission, investigating events surrounding the April Uprising. As part of their report, involving atrocities committed by the bashi-bazouk, an irregular military force, he brought the severed hand of a child to Istanbul, documenting what has come to be known as the 