PLO chief Yasser Arafat may have died of natural causes, but Israeli officials openly bragged of helping another leading terrorist on to his reward. On March 22, an Israeli helicopter gunship fired three missiles at a group of worshippers emerging from early morning prayers in Gaza. Among the eight casualties: Sheik Ahmed Yassin, the 67-year-old founder of the radical group Hamas, and two of his friends. The deaths of Mr. Yassin and Mr. Arafat left Palestinians in disarray at year's end, causing Middle East experts to predict months of infighting-and a chance for lasting peace.