Spc. Jeremy Morlock, of Wasilla, Alaska, is one of five defendants charged with murder and conspiracy in the deaths this year. Much of the Army's case is based on extensive statements Morlock gave describing the killings.
Last month, an investigating officer at Joint Base Lewis-McChord south of Seattle held a preliminary hearing in Morlock's case and recommended it proceed to a court martial.
The Army announced Friday that a court martial would be scheduled, though no timeframe was given, and that Morlock would face a maximum penalty of life in prison if convicted.
Neither announcement was a surprise. The military hasn't executed anyone since 1961, according to the Death Penalty Information Center.
Morlock, 22, cooperated with investigators and his lawyer said he suffered from repeat concussions from explosions in Afghanistan - both factors that could weigh against seeking execution, though the Army didn't detail its reasons.
"There's a lot of reasons they wouldn't seek the death penalty, especially when you have someone who has physical injuries from a combat zone," said Morlock's attorney Michael Waddington.
He said Morlock will fight the allegations at the trial and will seek to have his statements suppressed on the grounds that they were made under the influence of muscle relaxants and other drugs prescribed for possible traumatic brain injury.
No decision has been made on whether to send the other four defendants to trial or to seek the death penalty, Lewis-McChord spokeswoman Maj. Kathleen Turner said.
The allegations are some of the most serious to emerge from the Afghan war. In interviews with Army investigators, Morlock described a plot led by Staff Sgt. Calvin Gibbs to randomly kill civilians while on patrol in Kandahar Province. Gibbs denies the charges and insists all of the killings were appropriate engagements, his lawyer said.
Prosecutors have also alleged that members of the platoon mutilated and posed with Afghan corpses and even collected fingers and other body parts. Morlock talked about how they threw a grenade at one civilian to "wax him."
The killings occurred in January, February and May. In each, prosecutors said, Morlock and Gibbs enlisted one other soldier to be involved. Lawyers for those three said they either deny involvement or that their participation was unwitting.
The case raised serious questions about the Army's handling of it. Spc. Adam Winfield, who is charged in the final killing, sent troubling Facebook messages home to his parents in Florida after the first killing. He wrote that he was being threatened to keep his mouth shut about it and that he didn't know what to do.
His father made nearly half a dozen calls to military officials that day, and he said he warned them about the ongoing plot and the threats against his son.
But no arrests were made until May, when a witness in a drug case in the unit alerted investigators to what he considered unjustified killings.