JOINT BASE LEWIS-MCCHORD: A lone shooter could not have committed the massacre of 16 Afghan villagers blamed on a US soldier, a witness testified Sunday, stressing the scale of the atrocity.

The defence witness said the extent of the carnage, wrought overnight in two villages near a US army base in March, was too great for it to be the work of only Sergeant Robert Bales, facing a possible court martial.

“One person cannot do this work,” said Khudai Dad of the Afghan Uniform Police, who searched the scene of the killings the next morning. “One person doesn't have the courage to go from one village to another in the night.”

Bales, balding with close-cropped blond hair and wearing standard army combat uniform, showed no emotion as he watched the testimony on a small monitor placed in front of him.

He faces 16 counts of murder, six of attempted murder, seven of assault, two of using drugs and one of drinking alcohol. Seventeen of the 22 victims were women or children and almost all were shot in the head.

The 39-year-old allegedly left his base in the Panjwayi district of Kandahar province on the night of March 11 to commit the killings, which included nine children. He allegedly set several of their bodies on fire.

Prosecutors at a pre-trial hearing, held on an army base south of Seattle, have alleged that Bales left the base twice to carry out the killings, returning in between and even telling a colleague what he had done.

For the last three nights it has heard testimony by video link from southern Afghanistan, held at night to allow witnesses to give their accounts during the daytime.

Dad, the last witness to appear by video link, said he believed the two attacks must have happened simultaneously.

He said he went first to the US base, then to what was described as the first crime scene.

Although the Afghan National Army (ANA) were only supposed to secure the scene until he arrived, some shell casings were missing.

“The ANA was there before I (arrived). They picked up all the shell casings, all the rounds,” he said, adding that he himself had found a total of 13 shells.

In one house, “there was blood in the entrance when the woman came to the front door and was shot,” said Dad, slight man with a mustache and spectacles.

After searching three homes in the two villages involved, he said he was struck by the impression that more than one person would have had to be involved.

“I was thinking this is not a thing that one person can do,” he said, while adding that he believed the attacks occurred at the same time as each other, somewhere between midnight and 3:00 am.

Bales was flown from Afghanistan back to Fort Leavenworth, Kansas shortly after the alleged massacre, before being moved back to Fort Lewis-McChord recently, home base of the US 2nd Battalion, 3rd Infantry Regiment.

His wife and two children were moved to the sprawling military base south of Seattle for their own security, and to shield them from the glare of the media in the wake of the killings.

Before the hearings, Bales' wife reiterated her belief that he was innocent, saying he did not remember the shootings and was shocked when he was told details of the allegations against him.