MAHAWEEL, Iraq — Over a month's span 12 years ago, Iraqi soldiers loyal to Saddam Hussein took busloads of men, women and children — blindfolded and bound — down a dusty road outside the small town of Mahaweel. The soldiers pushed the people, possibly more than 3,000 of them, into trenches. They shot them and shoved dirt over their bodies. But one, a 12-year-old boy named Nasser, survived. The bullets missed him — twice — and he managed to crawl to a shallow end of the mass grave, where he bit through the rags that bound him. Yesterday, this apparent...