Staff Sgt. Robert Bales will be charged on Friday with 17 counts of murder and various other charges, including attempted murder, in connection with the March 11 attack on Afghan civilians, a senior United States official said on Thursday.
Sergeant Bales, who is 38 and had been serving his fourth combat tour overseas, is being held at Fort Leavenworth, Kan.
He is accused of walking away from his remote base in southern Afghanistan and shooting and stabbing members of several families in a nighttime ambush. At least nine victims were children and some others were women. Several sources said 16 people were killed, though some also said the number could be higher. The Army has not suggested a motive.
John Henry Browne, a lawyer for the soldier, has said that Sergeant Bales did not remember some events at the time of the attack. Mr. Browne said in interviews this week that the sergeant had not sought or received treatment for a concussion he apparently suffered during a vehicle rollover in Iraq in a previous deployment.
"There's definitely brain injury, no question about it," Mr. Browne said.
Mr. Browne said Thursday that he expected the charges.
"I'm not persuaded by many facts," he said. "There's no crime scene. There's no DNA. There's no confession, although they're leaking something, which I don't believe until I see it. This is going to be a hard case for the government to prove. And my client can't help me a lot with some of the things because he has mental problems and I believe they're totally legitimate."
The attack, most likely the deadliest war crime by a single American soldier in the decade of war that has followed the terrorist attacks of Sept. 11, 2001, has further frayed the relationship between the American and Afghan governments. Earlier this year United States military personnel burned Korans at an Afghan base, an act that prompted widespread public protests and a series of killings.
Gen. John R. Allen of the Marines, who commands the American-led allied forces in Afghanistan, told Congress this week that there would be an administrative investigation into the headquarters organization and the command of the sergeant's unit.
Sergeant Bales's legal proceedings could last years. He next faces an Article 32 hearing, in which the Army formally decides whether to press charges. If he is charged in an Article 32 hearing, he will most likely face a court-martial.
The sergeant has been based at Joint Base Lewis-McChord, south of Tacoma, Wash., when he was not deployed overseas. Although Sergeant Bales is being held in Kansas, Mr. Browne said Thursday that he believed there was a strong chance legal proceedings in the future could take place at Lewis-McChord.
Eric Schmitt contributed reporting.