JOINT BASE LEWIS-MCCHORD, Wash. -- A 22-year-old U.S. soldier pleaded guilty Wednesday to the murders of three unarmed Afghan civilians, telling a military judge "the plan was to kill people" in his coordinated conspiracy with four fellow soldiers.

Spc. Jeremy Morlock of Wasilla, Alaska, was court-martialed at Joint Base Lewis-McChord south of Seattle, where he pleaded guilty to three counts of murder, and one count each of conspiracy, obstructing justice and illegal drug use in exchange for a maximum sentence of 24 years in prison.

Morlock is a key figure in a war crimes probe that implicates a dozen members of his platoon and has raised some of the most serious criminal allegations to come from the war in Afghanistan.

He was accused of taking a lead role in the killings of three unarmed Afghan men in Kandahar province in January, February and May 2010.

Asked by the judge whether the plan was to shoot at people to scare them, or to shoot to kill, Morlock replied: "The plan was to kill people."

Morlock is the first of five soldiers from the 5th Stryker Brigade to be court-martialed -- something his lawyer Geoffrey Nathan characterized as an advantage.

"The first up gets the best deal," Nathan said by phone Tuesday, noting that even under the maximum sentence, Morlock would serve no more than eight years before becoming eligible for parole.

Under the plea deal, Morlock also has agreed to testify against his co-defendants.

Morlock told the judge, Lt. Col. Kwasi Hawks, that he and the other soldiers first began plotting to murder unarmed Afghans in late 2009, several weeks before the first killing took place.

To make the killings appear justified, the soldiers planned to plant weapons near the bodies of the victims, Morlock said.

"Did everybody know, `We're killing people who are completely innocent'?" the judge asked.

"Generally, yes, sir, everyone knew," Morlock replied.

Morlock told investigators the murder plot was led by Staff Sgt. Calvin Gibbs of Billings, Mont., who is also charged in the case; Gibbs maintains the killings were legitimate.

Morlock's mother and hockey coach were among the witnesses expected to testify Wednesday before Hawks, who will determine the soldier's sentence. Morlock's lawyers previously indicated they would argue that a lack of leadership in the unit contributed to the killings.

"He's really a good kid. This is just a bad war at a bad time in our country's history," Nathan said Tuesday.

"There was a lack of supervision, a lack of command control, the environment was terrible. In his mind, he had no choice."