It's unclear what prompted the killings, but the case has drawn new attention to the debate over mental-health care for the troops, who have had record suicide rates and high incidences of post-traumatic stress and brain injuries during repeated tours in Iraq and Afghanistan.
Six other Afghans - a man, woman, and four children - were wounded in Panjwai district of Kandahar province, the spiritual birthplace of the Taliban. Bales also was charged with six counts of attempted murder and six counts of assault in those cases, according to Col. Gary Kolb, a spokesman for U.S. forces in Afghanistan who disclosed information from the charging document.
Bales, of Lake Tapps, Wash., a father of two, was officially informed of the 29 charges just before noon local time at the U.S. military prison at Fort Leavenworth, Kan., where he is confined.
His civilian attorney, John Henry Browne, said Friday he believed the government would have a hard time proving its case and that his client's mental state would be an important issue. Bales was on his fourth tour of duty, having served three in Iraq, where he suffered head and foot injuries.
Browne has said his client remembers very little or nothing from the time the military believes he went on the rampage.
The decision to charge Bales with premeditated murder suggests prosecutors plan to argue that he consciously conceived the killings. A military legal official for U.S. forces in Afghanistan who spoke on condition of anonymity noted that murder does not have to be contemplated for long in order to qualify as premeditated.
The maximum punishment is death, dishonorable discharge from the armed forces, reduction to the lowest enlisted grade, and total forfeiture of pay and allowances, Kolb said. The mandatory minimum is life imprisonment with the chance of parole.
Legal experts have said the death penalty would be unlikely in Bales' case. The military hasn't executed a service member since 1961, when an Army ammunition handler was hanged for raping an 11-year-old girl in Austria. None of the six men currently on death row at Fort Leavenworth was convicted for atrocities against foreign civilians.
The charging document did not provide details about the killings, leaving the timeline unclear. The bodies were found in Balandi and Alkozai villages - one north and one south of the base.
The predawn shooting spree has further frayed ties between U.S. troops and President Hamid Karzai as the two nations are negotiating agreements for America's military presence in Afghanistan after most international combat forces withdraw by the end of 2014. After the shootings, Karzai reiterated his demand that foreign troops pull back to larger bases.
U.S. officials are working with Afghan officials to compensate relatives of the victims.