Camp Penleton, California: A marine sniper believed he was shooting at insurgents planting a roadside bomb when he killed two Syrians in Iraq, platoon members testified in military court.

Sergeant John Winnick II is charged with voluntary manslaughter and failing to adhere to the military's rules of engagement by firing without reasonable certainty that his targets were hostile.

Winnick, 24, also faces charges of aggravated assault against two other men injured in the June 17, 2007, shooting incident.

The shooting occurred during a surveillance operation, according to charging documents.

Winnick, who appeared in court on Tuesday, answered only procedural questions during the first day of the hearing before a Marine investigating officer, Captain Jeffrey King. At the conclusion of the hearing, King will recommend whether there is enough evidence to proceed to court-martial. If convicted, Winnick faces a maximum 40-year sentence.

At the time of the shooting, Winnick and his men had just arrived in Iraq and were watching an abandoned mosque and gas station in an area known for frequent roadside bomb attacks. Winnick fired after a soda delivery truck stopped on a highway at the same spot where two unidentified men had been seen apparently scoping out the area days before, said Corporal Alexander Wazenkewitz. Then all six marines on the team stormed out of an abandoned building, some shooting at the truck passengers with shotguns.

Wazenkewitz said he believed the possibility of a threat justified the use of force.