AFGHANISTAN - The United States is promising swift justice after a soldier allegedly went on a killing spree yesterday in an Afghanistan village near the base where he was stationed. A total of 16 civilians, including nine children and three women, were gunned down by the U.S. soldier, investigators say. His identity has not yet been released, but officials say he is a 38-year-old father of two who had already completed three tours in Iraq. The soldier left the compound where he was stationed before dawn Sunday, officials say. He entered private homes in a nearby village and opened fire, then burned some of their corpses. According to a senior Defense Department official, the soldier suffered a traumatic brain injury in 2010 but was deemed fit for duty after treatment.President Barack Obama has apologized and promised a thorough investigation, but Afghan President Hamid Karzai has called the shooting "unforgivable." The soldier has surrendered and is in U.S. custody, officials say.Afghan president: US soldier kills 16 civilians