Following this adventure, Burton prepared to set out in search of the source of the Nile, accompanied by Lieutenant Speke, Lieutenant G. E. Herne and Lieutenant William Stroyan and a number of Africans employed as bearers. The schooner delivered them to Berbera on 7 April 1855. While the expedition was camped near Berbera, his party was attacked by a group of Somali "waranle" ("warriors") belonging to Isaaq clan. The officers estimated the number of attackers at 200. In the ensuing fight, Stroyan was killed and Speke was captured and wounded in eleven places before he managed to escape. Burton was impaled with a javelin, the point entering one cheek and exiting the other. This wound left a notable scar that can be easily seen on portraits and photographs. He was forced to make his escape with the weapon still transfixing his head. It was no surprise then that he found the Somalis to be a "fierce and turbulent race". However, the failure of this expedition was viewed harshly by the authorities, and a two-year investigation was set up to determine to what extent Burton was culpable for this disaster. While he was largely cleared of any blame, this did not help his career. He describes the harrowing attack in "First Footsteps in East Africa" (1856).