The sister of a detained German-Egyptian activist said Egyptian police searched their house early Monday morning, four days after her brother's arrest and disappearance. Activist Philip Rizk, a 26-year-old graduate student of Middle Eastern studies at the American University in Cairo, was detained on Friday and his whereabouts are unknown. His sister Jeanette Rizk said Egyptian police spent three hours searching their home for books and documents before leaving at 4:30 a.m. local time, without taking any items. Rizk was detained after participating in a solidarity march for Palestinians in Gaza. Police have only confirmed his detention without providing further details.