    Sentence 1: Who was  Al-Banna's  assassination a retaliation for the prior  assassination of?    Sentence 2: Some elements of the  Brotherhood, though perhaps against  orders, did engage in violence against the  government, and its founder Al-Banna was  assassinated in 1949 in retaliation for the  assassination of Egypt's premier Mahmud  Fami Naqrashi three months earlier.