The military said it was investigating reports that a U.S. helicopter went down Friday north of Baghdad, while U.S. forces said they killed 18 insurgents after coming under attack in a volatile city west of the capital. Local officials in Hillah announced a three-day mourning period after two suicide bombers detonated explosives Thursday among shoppers in a crowded outdoor market in the Shiite city south of Baghdad, while police raised the casualty total to at least 73 people killed and 163 wounded. Full Story