The testimony came in the opening of a preliminary hearing for
Marine Sergeant Frank Wuterich, who faces 17 counts of murder over the Haditha killings, the most serious war crimes allegations faced by US troops in Iraq.
Wuterich, dressed in desert khakis, spoke confidently to confirm his name as the hearing to decide if he faces a court martial began at the Marines' Camp Pendleton base in southern California.
The 27-year-old listened intently as Lance Corporal Humberto
Mendoza recounted how Marines had responded after a roadside bomb attack on their convoy in Haditha on November 19, 2005 left one comrade dead.
Mendoza said Marines under Wuterich's command began clearing nearby houses suspected of containing insurgents responsible for the bombing.
At one house Wuterich gave an order to shoot on sight as Marines waited for a response after knocking on the door, said Mendoza.
'Well, shoot them'
During a subsequent search of the house, Mendoza said he received an order from another Marine, Lance Corporal Stephen Tatum, to shoot seven women and children he had found in a rear bedroom.
"When I opened the door there was just women and kids, two adults were lying down on the bed and there were three children on the bed … two more were behind the bed," Mendoza said.
"I looked at them for a few seconds. Just enough to know they were not presenting a threat … they looked scared."
After leaving the room Mendoza told Tatum what he had found.
"I told him there were women and kids inside there. He said 'Well, shoot them,'" Mendoza told prosecutor Lieutenant Colonel Sean Sullivan.
"And what did you say to him?" Sullivan asked.
"I said 'But they're just women and children.' He didn't say nothing."
Mendoza said he returned to a position at the front of the house and heard a door open behind him followed by a loud noise.
Returning later that afternoon to retrieve bodies, Mendoza said he found a room full of corpses.
In cross-examination, however, Major Haytham Faraj suggested a girl who survived the shootings had identified Mendoza as the gunman, sparking an angry reaction from prosecutors.
"The girl in question already identified another Marine," Sullivan stormed. "This is completely unethical, inappropriate and has no basis in fact."
Mendoza had given similar testimony during a preliminary hearing against Tatum earlier this year.
Investigating officer Lieutenant Colonel Paul Ware, who is presiding in Wuterich's hearing, last week recommended dropping murder charges against Tatum, describing Mendoza's evidence as "too weak".
Later in cross-examination, Mendoza praised Wuterich's leadership. "I think he's a great Marine, sir," he said.
'Killing spree' alleged
Prosecutors allege Marines went on a killing spree in Haditha in retaliation for the death of their colleague in the bomb attack.
Defence lawyers will argue that Wuterich followed established combat zone rules of engagement.
A total of eight Marines were initially charged in connection with the Haditha deaths.
Four were charged with murder while four senior officers were accused of failing to properly investigate the killings.
Of the four Marines charged with murder, two have since had charges withdrawn, while allegations against Tatum are also expected to be dismissed.
Wuterich also faces charges of making a false statement and asking another Marine to do the same. He faces a life sentence and dishonourable discharge if court-martialled.