The ringleader of a rogue US army unit accused of killing Afghan civilians for sport treated the locals like "savages," a court martial heard Monday.

The so-called "kill team" led by Staff Sergeant Calvin Gibbs was "out of control," prosecutors added as grisly photos of soldiers posing with a corpse were shown in court.

Gibbs, who sat expressionless in a tiny courtroom where the week-long case is being heard, also allegedly brandished fingers cut off dead bodies in a failed attempt to silence members of his team.

The 26-year-old faces life in prison if convicted on charges including three counts of premeditated murder, in a scandal that has threatened Abu Ghraib-style embarrassment for the US military.

Gibbs, the fourth member of the rogue unit to face court martial, is accused of staging killings between January and May 2010 to make them look like legitimate combat casualties.

Jeremy Morlock, described as Gibbs' "right hand man," said his former boss had frequent conversations about "drop weapons," or weapons found on the battlefield which could be planted on a body.

"He had a general disdain for Afghans, and called them savages," Morlock -- who agreed to testify against Gibbs as part of a deal in which he pled guilty in March -- told the court martial, expected to last a week.

Morlock told how Gibbs took over the platoon, stationed in volatile Kandahar province in southern Afghanistan, in November 2009, after its previous leader suffered serious injuries in a roadside bomb attack.

"We talked about payback," Morlock said, adding that the first "opportunity" took place on January 15, 2010 during a patrol of a village called La Mohammad Kalay.

Morlock said he and another soldier, Private Andrew Holmes, came across a teenage farmer alone in a field. They waved him over, and when he approached Morlock threw a grenade, and Holmes opened fire to make it look like a real firefight.

Photographs of the boy's bloody corpse were shown to the jurors, a five-member military panel. One of the pictures showed Morlock posing with the lifeless body.

The second alleged killing occurred on February 22 in the village of Kari Kheyl, when the platoon came across an unarmed local. Gibbs "asked if we were willing to kill this guy, smoke him," Morlock said.

With a contraband AK47, Gibbs "fires into a wall, then turns around and drops it, and then engages the individual with his M4 (rifle)," Morlock told the court martial.

The third alleged murder took place on May 2 in the village of Quala Day. Holding a grenade, Gibbs singled out an elderly man named Mullah Allah Dad and led him away from the compound where he lived with his wife and children.

At close range, "he tossed it (the grenade) at the individual and it exploded."

"Had he ever posed any sort of threat at any time?" asked Leblanc. "No sir" Morlock replied.

"How did Sergeant Gibbs react?"

"Not much, it was just another kill," Morlock said.

Gibbs' court martial opened last Friday with jury selection, after which Gibbs' lawyers entered not guilty pleas to all 16 charges at Joint Base Lewis-McChord, south of Seattle, home to the 5th Stryker Brigade.

Three of the other "kill-team" members have agreed to testify against Gibbs: Morlock, Specialist Adam Winfield -- as part of plea deals with prosecutors -- and Specialist Michael Wagnon.

In March, Morlock, 23, was jailed for 24 years and dishonorably discharged. In August, Winfield, 23, was sentenced to three years in prison, and in September, Holmes, 21, was jailed for seven years.

The alleged killings only came to light after another soldier, Private Justin Stoner, was warned by Gibbs brandishing fingers allegedly sliced off the hands of dead Afghans not to talk about hashish smoking in the platoon.

"He said if he didn't keep his mouth shut he'd end up like one of these guys," Morlock said.

Stoner soon went to investigators and began talking about the drugs, his own beating, and the killing of civilians. On May 12, Gibbs was arrested.