Alieu Kosiah was a commander of a faction of the United Liberation Movement of Liberia for Democracy (ULIMO) between 1993 and 1995. The ULIMO, which operated in Western Liberia since 1991, fought against the National Patriotic Front led by Charles Taylor during the First Liberian Civil War. The group managed to gain control over certain areas in the region, including Lofa county.
While Kosiah served as commander of the ULIMO, mass atrocities were committed by the ULIMO fighters. Kosiah allegedly directed and participated in the commission of systematic killings, rapes and forced labour of civilians in the Lofa county.
At the end of the Liberian Civil War in 1997, Kosiah moved to Switzerland, where he obtained permanent resident status.