As the morning sunlight crept over the limestone walls of Jerusalem's old city, two young Americans flagged down a bus and got on. It was 6:45 a.m., February 25, 1996 -- an otherwise ordinary Sunday in Israel. Two US citizens who were studying in Israel, Sara Duker and Matthew Eisenfeld, settled into their seats as the door closed on Jerusalem's Number 18 bus which would take them across the spine of this ancient city of hills. On this day, they had...