The shootings occurred June 17, 2007, near Lake Tharthar in the Anbar province. Winnick is giving his account of the incident through an unsworn statement, which means he cannot be cross-examined. The proceedings are taking place in a courtroom at Camp Pendleton.

Winnick, 24, is accused of firing before identifying the civilians as insurgents or confirming that they posed a threat to him or members of his sniper team. He is charged with voluntary manslaughter, aggravated assault and failure to obey orders or regulations.

If convicted, he could be imprisoned for 40 years and receive a dishonorable discharge.

Winnick was a San Diego native who graduated from The Winston School in Del Mar in 2002. He pre-enlisted in the Marine Corps at age 17.

After one of his deployments to Iraq, Winnick was promoted from the rank of lance corporal to corporal for shooting a person who was planting a roadside bomb.

He was on his fourth combat tour when the Lake Tharthar shootings happened. On Tuesday, a member of the sniper team recalled the events of the day in question.

Winnick and five other snipers were monitoring a highway intersection where insurgents were known to plant improvised explosive devices, said Sgt. Algt. Alex Wazenkewitz, a member of the group.

At some point, Wazenkewitz testified, a car stopped and a man got out and “messed with the ground” before leaving. A bit later, another vehicle stopped on the side of the road opposite from where the first car had parked, he said.

After the second vehicle left, a big-rig stopped in the same vicinity. A man came out and appeared to take a satchel from the truck.

“We are thinking this is coordinated. They are probably going to (plant) an improvised explosive device,” Wazenkewitz testified.

Winnick shot the man near the truck with his sniper rifle, grabbed a shotgun to lead his team's assault on the big-rig and fired more rounds, Wazenkewitz said.

One man died from a shot to the head, another was shot in the stomach and a third suffered some type of injury, Wazenkewitz testified.

Another witness said Tuesday that a search of the big-rig's cab and the area around the truck yielded no evidence of bomb-making. The Marines did not check the trailer before the big-rig was removed from the scene several hours later.

Two major issues in the case are whether Winnick was following the military's rules of engagement, and whether those regulations are confusing or overly complex.

Lt. Dominic Corabi, Winnick's platoon commander in Iraq, testified Tuesday that even senior officers couldn't agree about when a Marine could use deadly force. Corabi said he disregarded the advice of his battalion's executive officer and followed the guidance of the unit's lawyer, who said Marines should use lethal force if they deemed it necessary.

“The general consensus was that if you took a shot, there was going to be a big investigation,” Corabi testified. “I said (to snipers) to basically do your best. Make these decisions as best you can, and I will support you.”

Capt. Jeffrey King is overseeing Winnick's Article 32 session. Later on, he will recommend to Lt. Gen. Samuel Helland, the convening authority in the case, whether Winnick should go to trial.

Winnick is a member of the Camp Pendleton-based 3rd Battalion, 1st Marine Division. He was working with the 13th Marine Expeditionary Unit, also based at Camp Pendleton, when the Lake Tharthar incident took place.

His battlefield exploits in the 2004 battle of Fallujah, Iraq, caught the eye of author Bing West.

In the book “No True Glory: A Frontline Account of the Battle for Fallujah,” Bing described the intensity of the fighting and Winick's actions: “They rushed down to the street. As they moved up the alley, Lance Cpl. John Winnick, a machine-gunner, ran toward (Lt. Jesse) Grapes with a (rocket-propelled grenade) launcher and a bag full of rockets.”

“Sir, can I shoot these back at them?” Winnick yelled.

“Do you know how to use that thing? PI: Winnick had never held or fired the launcher during combat, but he convinced Grapes to let him use it then. He fired twice, blowing open a gate and then hitting a fuel drum inside a house as Marines cheered.

“In minutes the fire had spread through the first floor, and the insurgents had fled,” Bing wrote.

Winnick's family and friends have create a Web site to support him and seek donations for his legal defense.

Five Marines posted comments on the site, including Wazenkewitz.

“I was at John's side on June 17th and I would have done everything exactly the same. He did nothing wrong,” Wazenkewitz wrote. ”I have nothing but respect for that man and would take a bullet for him any day.”