NAJAF, Iraq - The murder of a pro-Western cleric in this holy city two weeks ago removed America's most promising Shiite Muslim ally and now threatens to fracture Iraq's Shiite majority into warring factions. As accusations reverberate over who was behind the violence, a senior religious authority of the Grand Imam Ali Mosque, where Shiite leader Abdul Majid al Khoei was killed on April 10, said the murderers were followers of Moqtada al Sadr, a fiery young Shiite cleric. Jabar Khanee Jaafer, the mosque's deputy custodian, described the murder in an exclusive and emotional interview with a Knight Ridder...