An Army staff sergeant described by a comrade as 'evil incarnate' cut fingers off the corpses of three Afghan civilians — but he had nothing to do with any plot to slaughter those unarmed men for sport, his lawyer said on Monday.

A court martial opened for Staff Sgt. Calvin Gibbs who has pleaded not guilty to 16 criminal charges ranging from murder to taking the fingers as bloody mementos.

He maintains that, as far as he knew, the three killings early last year were legitimate engagements — and that his co-defendants conspired to blame him when they got caught.

"What you are seeing in this case is the ultimate betrayal of an infantryman," Gibbs' attorney, Phil Stackhouse, told jurors in his opening statement.

In some of the most gruesome allegations to emerge from the Afghan war, prosecutors say Gibbs and his co-defendants slaughtered the victims with grenades and powerful machine guns during patrols in Kandahar province, then dropped weapons near their bodies to make them appear to have been combatants.

Of the five soldiers charged as part of the so-called 'kill team' within the platoon, three have pleaded guilty and agreed to testify against Gibbs, who faces up to life in prison without parole if convicted.

Gibbs, 26, is the highest-ranking of those charged. Others in the unit, including some of his co-defendants, portrayed him as an imposing sociopath with little respect for life — a man who gunned down dogs without provocation, threatened fellow soldiers and who tallied his kills with skull tattoos on his calves.

Another lead figure in the plot, Pvt. Jeremy Morlock, has testified that Gibbs played with the corpse of the first victim, a teenager, as if it was a puppet. The jurors were shown graphic photographs, including one in which Morlock stood over the victim's body and held up his head as though he had just bagged a deer.

A prosecutor, Capt. Dan Mazzone, told the jurors at Joint Base Lewis-McChord south of Seattle that Gibbs took advantage of weak leadership in the platoon to lead his juniors into the diabolical plot. This wouldn't be a case where they have to second-guess difficult combat decisions, Mazzone told them.

"This case is the exact opposite: It is about premeditated murder," Mazzone said.

Gibbs joined the unit in what was then known as the 5th Stryker Brigade in Kandahar province in late 2009. He soon began telling others how easy it would be to kill civilians, Mazzone said.

And when the platoon later came across a body that had been mangled by a helicopter gun, Mazzone said, Gibbs had reason to believe he'd really be able to get away with murder: As the platoon's leadership watched, one soldier stabbed the corpse with a knife and posed for a photo.

"This platoon is out of control," Mazzone said.

"He sees weak leaders, he sees an opportunity, he sees soldiers who are willing to cross the line."

Gibbs' lawyer sought to lay the blame for any unjustified killings with Gibbs' comrades. When Gibbs came to the unit, hash smoking was already rampant, Stackhouse said.

Gibbs, who had more combat experience than most of the others, did talk frequently of previous shootings he'd been involved in — including one in Iraq, when Gibbs fired on a car that refused to stop at a checkpoint, only to later learn that the vehicle was carrying an innocent Iraqi family.

The others may have misinterpreted Gibbs' stories, Stackhouse suggested.

"On hash-filled nights, under a cloud of intoxication ... they'd talk about these things," he said.

Stackhouse admitted in his opening statement that Gibbs took fingers from the victims. He noted that while it's inappropriate to take such trophies, soldiers are taught to disassociate war casualties from the human being they once were.

Gibbs is accused of a wide range of misconduct, from providing a grenade used in January 2010 to kill the first victim, an unarmed farmer in a field in Kandahar province, to directly shooting or tossing grenades at the next two in February and May of that year.

One co-defendant, then-Cpl. Morlock of Wasilla, Alaska, said that he or Gibbs enlisted one other soldier to participate in each of the three killings.