CAMP PENDLETON, California — A former squad mate of a Marine implicated in the deaths of 19 Iraqis testified Tuesday that after a roadside bombing, the group raced to nearby homes, firing rounds and tossing grenades, even though he heard no gunfire and saw no weapons or Iraqis fleeing.

Former Cpl. Steven Tatum gave his account at the Camp Pendleton trial of Staff Sgt. Frank Wuterich, who faces nine counts of manslaughter for the deaths of civilians, including unarmed women and children, in the town of Haditha in 2005.

Wuterich is the last defendant in one of the biggest criminal cases against U.S. troops from the war. Prosecutors have implicated him in 19 of 24 Iraqi deaths.

Wuterich's attorneys say the squad came under fire after a bomb killed one Marine, prompting him to order troops to clear the homes.

Prosecutors and defense attorneys agree the explosion that killed Lance Cpl. Miguel Terrazas on Nov. 19, 2005, influenced Wuterich's decisions that day.

The debate is whether Wuterich reacted appropriately as a Marine squad leader in protecting his troops in the midst of a chaotic war or went on a vengeful rampage, disregarding combat rules and leading his men to shoot and blast indiscriminately at Iraqi civilians.

Tatum testified on the second day of before an all-Marine jury at Camp Pendleton.

Prosecutors in their opening statement Monday painted a picture of a young Marine with no prior combat experience losing control after seeing his friend's body blown apart.

They showed jurors — all of whom have combat experience in Iraq — graphic pictures of bodies, including the faces of men shot at mid-range who were in a car near the scene of the bomb attack, and described how Wuterich stood at the foot of a bed of a frightened woman and children in one of the home's back bedrooms and sprayed them with bullets.

Maj. Nicholas Gannon, the prosecutor, said the evidence will show Wuterich "never lost control of his squad ... but he made a series of fatal assumptions and he lost control of himself."

Wuterich has said he regretted the loss of civilian lives but believed he was operating within military combat rules.

Wuterich's lawyers said the squad was under small arms fire and Wuterich believed insurgents were in the homes. Attorney Haytham Faraj asked jurors to apply their Marine Corps knowledge and combat experience and imagine how they would react after the deadly blast, blinded by the debris and believed to be under attack.

Faraj, a retired Marine, told the jury of four enlisted men and four officers that Wuterich's orders were meant to urge Marines not to hesitate in reacting.

He also told jurors not to be swayed by Wuterich's squad members who testify against him, accusing the government of influencing them by offering to dismiss charges against them.

"You have a bunch of scared Marines promised immunity who are going to tell you about things that did not happen," Faraj said.

Wuterich, who has been working a desk job at Camp Pendleton awaiting the long-delayed trial, is the last of eight Marines initially charged. Six have had their charges dismissed or discharged. One was acquitted.

Military investigators told jurors Wuterich told them repeatedly that he instructed his squad to "shoot first, ask questions later." Wuterich also acknowledged that he did not positively identify his targets, three investigators testified.

Investigators said they were shocked to hear such a disregard of the rules on when to apply deadly force.

"It seemed to show a lack of discipline and that essentially there were no rules...and that concerned me," testified Army Lt. Col. David Mendelson, who helped to initially investigate the case. "For me it placed in context the rest of the day in terms of potentially why so many women and children got killed from there on out."

The trial was delayed for years by legal wrangling over unaired outtakes of a 2007 interview Wuterich gave to CBS "60 Minutes." Ultimately prosecutors won their right to view them.

Parts of the interview were used in the prosecution's opening statement, including a reference to Wuterich saying every Marine in his squad acted as ordered and did their job.