They believed he might have started the Ghost Dance Movement because of his firce opposition to Anglo-Americans influence on the lives of Native Americans.
The Lakota Sioux chief, Sitting Bull, was one of the most influential leaders of the great plains. He was involved in many battles and the Standing Rock Indian Agency feared that he might incite the Sioux and others to rebel.
When the mystical Ghost Dance ritual started in 1890, the Agents feared it might lead to an Indian uprising. They wrongly believed Sitting Bull was the driving force behind it because of his influence in the tribe. He was shot by an Indian Agent among fears he might escape the reservation with Ghost Dance followers and form some type of armed resistance.
The real founder of the Ghost Dance was a Paiute Indian from Nevada called Wovoka, also known as Jack Wilson.