A witness to the killing spree that left 16 Afghan civilians dead spoke of how the rogue American soldier responsible for the deaths moved from room to room looking for his victims.

"I heard a gunshot. When I came out of my room, somebody entered our house," a 26-year-old villager named Mohammad Zahir said.

"After that, I saw him moving to different areas of the house – like he was searching." Mr Nazir's father, unarmed, then took a few steps out of his bedroom. Then the soldier fired.

The harrowing account of the attack came as tribal elders, local councillors and relatives of the men, women and children killed in their homes by the rogue soldier warned yesterday of violent protests in the Afghan city of Kandahar if the US did not act swiftly to prosecute the shooter.

Haji Aghalalai Dastgiri, an elder from Panjwai and a member of Kandahar's provincial council, told The Independent: "People [at the meeting] requested that either the US government or the Afghan government prosecute the killer as soon as possible. If not, there will be an attack on the US base." Afghan parliamentarians called for the soldier to be tried in an Afghan court. The threat came as more details emerged about the identity of the suspected killer.

He is believed to be an Army staff sergeant who has spent more than 10 years in the US forces and completed multiple tours in Iraq.

It emerged yesterday that the soldier had a traumatic brain injury at one point and had problems at home after his last deployment, officials told ABC News.

After returning from his last deployment in Iraq, he had difficulty reintegrating, according to the reports, but officials said he "worked through" those issues before deploying to Afghanistan.

He is accused of walking out of the Zangabad base in Kandahar's Panjwai district early Sunday morning before going on his murderous spree. Nine children were among the dead.

Despite assertions from US officials, participants at yesterday's gathering insisted that it was impossible that the attack had been carried out by a lone soldier, given the distance between the villages where the atrocities occurred.

Abdul Rahim Ayoubi, a Kandahar MP, said after the meeting that there was evidence of more than one killer from footprints found at the scene.

Members of the Afghan National Security Forces were a visible presence in the Panjwai district yesterday, preventing widespread grief erupting into potentially violent demonstrations. "I buried all my four family members yesterday," Habibullah Khan said. "And today we are completing the other Islamic ceremony – to read Korans for them in the mosques. Yesterday was the saddest day for me. The US soldiers took my life. Sometimes I think about going to their base to do a suicide bombing."