A military jury is considering its verdict in the trial of a US soldier accused of leading a "kill team" in Afghanistan which murdered unarmed civilians and collected body parts as war trophies.

Staff sergeant Calvin Gibbs, 26, faces a range of charges including murder, assault and conspiracy over the killings of three Afghans in separate incidents last year, in situations allegedly staged to look as if the victims were combatants.

In one of the most serious accusations of war crimes to emerge from the Afghan conflict, Gibbs is alleged to have recruited other soldiers to murder civilians he called "savages" after he took over command of a US army platoon in Afghanistan's Kandahar province in November 2009.

The military prosecutor, major Rob Stelle, told the court: "Sergeant Gibbs had a charisma, he had a 'follow me' personality. But it was all a bunch of crap, he had his own mission: murder and depravity. No one died before Sergeant Gibbs showed up".

Gibbs is accused of inciting two soldiers to kill 15 year-old Gul Mudin, who was working in a field. Gibbs allegedly gave a grenade to one of the soldiers, Jeremy Morlock, who threw it at Mudin. A second soldier, Andrew Holmes, then shot the boy. Gibbs played with the corpse of the teenager "as if it was a puppet", Morlock told the trial.

Gibbs and another soldier, Michael Wagnon, are alleged to have shot dead a man sleeping by a roadside, Marach Agha, and then to have planted a Kalashnikov next to the corpse to make it look as if he was a fighter. Gibbs allegedly kept part of the victim's skull as a trophy.

Gibbs, Morlock, and a third soldier, Adam Winfield, allegedly killed a Muslim cleric, Mullah Adahdad, with a grenade and then shot him.

The soldiers are alleged to have collected fingers, teeth and other body parts as trophies. They also took photographs of themselves posing next to their dead victims. In one of the pictures, Morlock is seen lifting Mudin's head by its hair for the camera, and smiling. The soldiers also took ghoulish pictures of themselves with dead combatants.

The jury of five soldiers was shown pages of Facebook messages sent by Winfield to his parents in which he describes how Gibbs led the killings. In one exchange with his father, Winfield recounted Mudin's killing.

"An innocent dude. They planned and went through with it. I knew about it. Didn't believe they were going to do it. Then it happened. Pretty much the whole platoon knows about it. It's OK with all of them, pretty much. Except me. I want to do something about it. The only problem is I don't feel safe here telling anyone. The guy who did it is the golden boy in the company who can never do anything wrong, and it's my word against theirs," Winfield wrote.

Winfield later told investigators: "[Gibbs] likes to kill things. He is pretty much evil incarnate. I mean, I have never met a man who can go from one minute joking around, then mindless killings."

The court martial was told that Gibbs has six skull tattoos on his leg to mark up each of his "kills" from tours in Iraq and Afghanistan.

In his testimony, Gibbs denied responsibility for the killings, but did admit to slicing off body parts from Afghans, including the fingers of a man, and keeping them or giving them to other soldiers as trophies.

"In my mind, I was there to take the antlers off the deer. You have to come to terms with what you're doing. Shooting people is not an easy thing to do," said Gibbs.

The prosecution witnesses against Gibbs included members of his army unit who were also involved in the atrocities. Morlock and Holmes have pleaded guilty to murder and received prison sentences of 24 years and seven years respectively. Winfield pleaded guilty to involuntary manslaughter for failing to prevent other soldiers from attacking Afghan civilians. He was jailed for three years.

Wagnon is awaiting trial over the killings and collecting human body parts.

A defence lawyer, Phil Stackhouse, told the court martial that other soldiers were framing Gibbs to diminish their own crimes and receive lesser sentences.

"The witnesses that came in here, the core group, traded their testimony for years of their lives, years of their lives," he said.

Stackhouse said there was no physical evidence against Gibbs and that other soldiers' recollections were clouded by a "haze of hashish".

The killings came to light in May after the army began investigating an assault on a soldier, Justin Stoner, after he reported to superiors that members of his unit were smoking hashish. Gibbs, Morlock and other members of the platoon are alleged to have beaten Stoner and told him to keep his mouth shut. Stoner reported the beating and told investigators what he knew of the "kill team".

Gibbs faces a mandatory sentence of life in prison without parole if convicted on any of the most serious charges.