BAGHDAD - U.S. soldiers found mass graves north of Baghdad next to a torture center where chains were attached to blood-spattered walls and a metal bed frame was still connected to an electrical shock system, the military said Thursday. Separately, at least 13 Iraqis were killed when a suicide bomber targeted a group of people who had gathered around U.S. soldiers handing out holiday gifts, local authorities said. It was not immediately known if any soldiers were killed or wounded. The grisly discoveries of the mass graves and torture center near Muqdadiyah, about 60 miles north of Baghdad, came during...