JOINT BASE LEWIS-McCHORD, Wash. » A soldier accused of killing Afghan civilians for sport was sentenced to 24 years in prison yesterday, after he pleaded guilty and agreed to testify against other defendants in the case.

Spc. Jeremy Morlock, one of five soldiers from an Army Stryker brigade based here who is accused of staging combat situations to kill three civilians in Afghani­stan last year, told the military judge presiding over the case, Lt. Col. Kwasi Hawks, that the deaths were neither justified nor accidental.

"The plan was to kill people, sir," Morlock told the judge at the start of a court-martial proceeding here.

The sentence, plea and agreement to testify followed an agreement Morlock and his lawyers negotiated with prosecutors in January. The typical sentence for the charges to which he pleaded guilty — including three charges of premeditated murder, conspiracy to commit murder and assault — is life in prison, with or without the possibility of parole.

Morlock, 22, of Wasilla, Alaska, is the first of the five to face a court-martial.

Few new details emerged in the proceeding. Morlock had already given several interviews to investigators, including some on videotape that have been broadcast nationally, in which he described how members of his unit, part of a brigade deployed to Afghanistan in 2009 and 2010, used grenades and rifles to fake combat situations so they could kill civilians who he said posed no threat.

In court yesterday, Morlock affirmed the accuracy of statements he had signed earlier in which he claimed that another of the accused, a superior, Staff Sgt. Calvin Gibbs, was the ringleader in the killings. A lawyer for Gibbs has said all the killings were justified combat situations.

Morlock apologized to families of the victims and to "the people of Afghanistan themselves," as well as to fellow soldiers.

Some soldiers in the case are accused of posing with dead Afghans in photographs and then sharing the pictures with others. This week, German magazine Der Spiegel published three photographs, including one that appears to show Morlock smiling as he holds the head of a dead man by the hair.

Platoon member Spc. Adam Winfield sent Facebook messages to his parents after a killing in January saying that his fellow soldiers had murdered a civilian and were planning to kill more. Winfield said his colleagues warned him not to tell anyone.

Winfield’s father alerted a staff sergeant at Lewis-McChord, but no action was taken until May, when a witness in a drug investigation in the unit reported the deaths.

Winfield is accused of participating in the final murder. He admitted in a videotaped interview that he took part and said he feared the others might kill him if he didn’t.

Also charged in the murders are Pfc. Andrew Holmes and Spc. Michael Wagnon II.

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The Associated Press and New York Times contributed to this report