The committee elected Major Mengistu Haile Mariam as its chairman and Major Atnafu Abate as its vice-chairman. The Derg was initially supposed to study the grievances of various military units, and investigate abuses by senior officers and staff, and to root out corruption in the military. In the months following its founding, the power of the Derg steadily increased. In July 1974 the Derg obtained key concessions from the Emperor, Haile Selassie, which included the power to arrest not only military officers, but government officials at every level. Soon both former Prime Ministers Tsehafi Taezaz Aklilu Habte-Wold, and Endelkachew Makonnen, along with most of their cabinets, most regional governors, many senior military officers and officials of the Imperial court found themselves imprisoned.