A U.S. soldier accused of exhorting his bored underlings to slaughter three civilians for sport was convicted of murder, conspiracy and other charges Thursday in one of the most gruesome cases to emerge from the Afghan war.

The military jury sentenced Army Staff Sgt. Calvin Gibbs, of Billings, Mont., to life in prison, but he will be eligible for parole in less than nine years.

Gibbs was the highest ranking of five soldiers charged in the deaths of the unarmed men during patrols in Kandahar province early last year. At his seven-day court martial at Joint Base Lewis-McChord south of Seattle, the 26-year-old acknowledged cutting fingers off corpses and yanking out a victim's tooth to keep as war trophies, "like keeping the antlers off a deer you'd shoot."

But he insisted he wasn't involved in the first or third killings, and in the second he merely returned fire.

Prosecutors said Gibbs and his co-defendants knew the victims posed no danger but dropped weapons by their dead bodies to make them appear to have been combatants.

Three of the co-defendants pleaded guilty, and two of them testified against him, portraying him as an imposing, bloodthirsty leader who in one instance played with a victim's corpse and moved the mouth like a puppet. Gibbs' lawyer insisted they conspired to blame him for what they had done and told the five jurors the case represented "the ultimate betrayal of an infantryman."

The jury deliberated for about four hours before convicting him on all charges. The sentencing hearing began immediately after the verdict was announced, with a prosecutor, Maj. Andre LeBlanc, asking for the maximum, life without parole. He told jurors that Gibbs was supposed to protect the Afghan people but instead caused many to lose trust in Americans, hurting the mission. LeBlanc noted that Gibbs repeatedly called the Afghans "savages."

"Ladies and gentlemen, there is the savage -- Staff Sgt. Gibbs is the savage," he said.

Gibbs' lawyer, Phil Stackhouse, asked for leniency -- life with parole, instead of without it -- and noted that Gibbs could be eligible for parole after 10 years if they allowed it.

"He'd like you to know he has had failures in his life and he's had a lot of time to think about them," Stackhouse said. "He wants you to know he's not the same person he was in Afghanistan.

He doesn't want his wife to have to raise their son on her own."

The investigation into the 5th Stryker Brigade unit exposed widespread misconduct -- a platoon that was "out of control," in the words of a prosecutor, Maj. Robert Stelle. The wrongdoing included hash-smoking, the collection of illicit weapons, the mutilation and photography of Afghan remains, and the gang-beating of a soldier who reported the drug use.

In all, 12 soldiers were charged; all but two have now been convicted.

The probe also raised questions about the brigade's permissive leadership culture and the Army's mechanisms for reporting misconduct.

After the first killing, one soldier, then-Spc. Adam Winfield, alerted his parents and told them more killings were planned, but his father's call to a sergeant at Lewis-McChord relaying the warning went unheeded. Winfield later pleaded guilty to involuntary manslaughter in the last killing, saying he took part because he believed Gibbs would kill him if he didn't.

The case against Gibbs relied heavily on testimony from former Spc. Jeremy Morlock, of Wasilla, Alaska, who is serving 24 years after admitting his involvement in all three killings.

According to Morlock, Gibbs gave him an "off-the-books" grenade that Morlock and Pfc. Andrew Holmes, of Boise, Idaho, used in the first killing -- a teenager in a field -- in January 2010.

The next month, Morlock said, Gibbs killed the second victim with Spc. Michael Wagnon, of Las Vegas, and tossed an AK-47 at the man's feet to make him appear to have been an enemy fighter. Morlock and Winfield said that during the third killing, in May, Gibbs threw a grenade at the victim as he ordered them to shoot.

Morlock and others told investigators that soon after Gibbs joined the unit in 2010, he began talking about how easy it would be to kill civilians, and discussed scenarios where they might carry out such murders.

Asked why soldiers might have agreed to go along with it, Morlock testified that the brigade had trained for deployment to Iraq before having their orders shifted at the last minute to Afghanistan.

The infantrymen wanted action and firefights, he testified, but instead they found themselves carrying out a more humanitarian counter-insurgency strategy that involved meetings and handshaking.

Another soldier, Staff Sgt. Robert Stevens, who at the time was a close friend of Gibbs, told investigators that in March 2010, he and others followed orders from Gibbs to fire on two unarmed farmers in a field; no one was injured. Gibbs claimed one was carrying a rocket-propelled grenade launcher, but that was obviously false, Stevens said.

Stevens also testified that Gibbs bragged to him about the second killing, admitting he planted an AK-47 on the victim's body because he suspected the man of involvement with the Taliban, according to a report on the testimony in The News Tribune newspaper of Tacoma.

But during the trial, Gibbs insisted he came under fire.

"I was engaged by an enemy combatant," he said. "Luckily his weapon appeared to malfunction and I didn't die."

Gibbs testified that he wasn't proud about having removed fingers from the bodies of the victims, but said he tried to disassociate the corpses from the humans they had been as a means of coming to terms with the things soldiers are asked to do in battle.

The muscular 6-foot-4 staff sergeant also testified that he did it because other soldiers wanted the trophies, and he agreed in part because he didn't want his subordinates to think he was a wimp.

Gibbs initially faced 16 charges, but one was dropped during the trial.