Livingstone proposed to prove that the Lualaba connected to the Nile, but on 15 July, he witnessed a massacre of about 400 Africans by Arab slavers in Nyangwe, which experience left him too horrified and shattered to continue his mission to find the sources of the Nile, so he turned back to Lake Tanganyika.
Livingstone propuxo demostrar que o Lualaba conectaba co Nilo, pero o 15 de xullo, foi testemuña da masacre duns 400 africanos por escravistas árabes en Nyangwe, unha experiencia que o deixou demasiado arrepiado e disuadiuno de continuar a súa misión de atopar as fontes do Nilo, polo que volveu de novo ao lago Tanganica.