BAGHDAD -- As a U.S. Army patrol rolled into Sadr City one night in August, soldiers received a tip that militants in dump trucks were planting roadside bombs.
American troops had been clashing regularly with Al Mahdi militiamen in the restive Baghdad slum. So when Staff Sgt. Cardenas Alban of Carson saw an object fall from a garbage truck in the distance, his company took positions around the vehicle and unleashed a barrage of fire from rifles and a 25-millimeter cannon atop a Bradley fighting vehicle. The truck exploded in flames.
As soldiers from the 1st Battalion, 41st Infantry Regiment, approached the burning vehicle, they did not find insurgents. The victims were mainly teenagers, hired to work the late shift picking up trash for about $5 a night, witnesses said.
Medics scrambled to treat the half-dozen people strewn around the scene. A dispute broke out among a handful of soldiers standing over one severely wounded young man who was moaning in pain. An uninjured Iraqi claiming to be a relative pleaded in broken English for soldiers to help the victim.
But to the horror of bystanders, Alban, 29, a boyish-faced sergeant who joined the Army in 1997, retrieved an M-231 assault rifle and fired at the wounded man.
Seconds later, another soldier, Staff Sgt. Johnny Horne Jr., 30, of Winston-Salem, N.C., grabbed an M-16 rifle and also shot the victim.
The killing might have been forgotten but for a U.S. soldier who days later slipped an anonymous note under the door of the unit's commander, Capt. Robert Humphries, alleging that "soldiers had committed serious crimes that needed to be looked at."
U.S. officials have since characterized the shooting as a "mercy killing," citing statements by Alban and Horne that they shot the wounded Iraqi "to put him out of his misery."
Military attorneys, however, are calling it premeditated murder and have charged the two sergeants, saying the victim's suffering was no excuse for the soldiers' actions.
"I have no doubt that's why they did it," said Capt. John Maloney, one of the military attorneys prosecuting the case.
"But it still constitutes murder."
Military attorneys in Baghdad said they were unaware of any legal precedent justifying "mercy killing" in a war zone, though such circumstances could be considered during sentencing.
Iraqis who witnessed the Aug. 18 shooting said that rather than provide medical help to an injured civilian, the soldiers treated the Iraqi as if he were an animal struck by a car.
"We are not sheep," said Emad Raheem, 40, who said he was the driver of the dump truck. "We are human beings."
Seven Iraqis were killed in the attack, including the one who was shot, military officials said. Eight others were wounded.
Alban and Horne -- both on their second tour in Iraq -- and their attorneys declined to comment. In statements to military investigators, both acknowledged shooting the Iraqi but have not entered formal pleas. They are facing Article 32 hearings in Baghdad, which will determine whether there is enough evidence to begin court-martial proceedings. If convicted, the soldiers could receive the death penalty.
The case -- one of about a dozen murder cases filed against U.S. troops in Iraq -- is fueling a debate about the conduct of American forces here and the treatment of Iraqi civilians, particularly in the aftermath of the Abu Ghraib prison scandal.
Two other soldiers in Alban's unit, from Ft. Riley, Kansas, also are under investigation for what military officials say were the premeditated murders of three Iraqi civilians in separate cases.
In September, a U.S. reservist was sentenced to 25 years for killing a teenage Iraqi national guard soldier after a sexual encounter in an observation tower. The soldier said he lost control because of traumatic memories of childhood abuse, but family members of the victim accused the American of assaulting the Iraqi and then shooting him to cover it up.
"These crimes represent the pinnacle of American oppression and violence," said Mudaffar Battat, editor of a Sadr City newspaper.
The identity of the Iraqi killed by Alban and Horne remains unclear. U.S. military officials say they can't verify the individual's name because they never collected his personal information, did not interview or compensate family members and then lost track of his body. They suspect that his body was taken by Iraqi police and buried.
Iraqi witnesses found by The Times identified the victim as Qassim Hassan, 16, who had joined his brother and several cousins that night to earn extra money. They said their group of 15 was traveling in three dump trucks about 1:30 a.m. and had just passed through a military checkpoint when they were attacked.
"Most of [the victims] were poor teenagers," said Heider Ali Ismail, 21, who drove one of the trucks. "We were finishing up and just about to unload the trucks."
Hassan sat in the back of one of the trucks amid the rubbish, which ignited after the American soldiers fired.
Hassan's cousin, Ahmed Majid, said in an interview that Hassan's clothing caught fire and he struggled to jump off the truck, falling to the ground unconscious.
Military officials would not confirm whether Hassan was the same person shot by the soldiers. Majid and Raheem said they had been invited to testify at a military hearing Saturday.
Accounts of the incident by U.S. and Iraqi witnesses bear some similarities, but the two sides disagree on other aspects of the attack, including the extent of injuries suffered by the Iraqi.
Alban and Horne said in confessions that the man they shot was severely wounded and unlikely to survive. They said they watched him moan and writhe in pain until they could stand it no longer.
Sgt. Jacob E. Smith, an Army medic who helped treat the wounded Iraqis, testified that the victim's limbs were severely burned and his intestines were spilling out.
"Everything from his ribs to his hips was gone," Smith said. "He was in bad shape. He was going to die." Another witness said the man's spinal cord was exposed.
Majid said his cousin was unconscious and struggling to breathe, but his only injuries were burns. He said he pleaded with soldiers to help his cousin and his brother, who was still trapped in the burning truck. But when he tried to help Hassan, he said, a soldier pushed him away, saying, "Shut up and go!" Then the soldier shot his cousin, he said.
After the shooting, Majid said he saw two soldiers appearing to argue about the incident.
At a recent military hearing in Baghdad, an Army gunner, Spc. William Davis, testified that the two sergeants initially asked him to shoot the wounded Iraqi. Davis said he refused.
He described how an uninjured Iraqi male pleaded with Horne not to kill the wounded Iraqi on the ground.
"The guy was saying, 'No,' " Davis testified. " 'He's my brother! He's my brother!' "
According to Davis, Horne replied, "I understand, but he's gone."
Then, after consulting with the platoon leader and briefly debating what sort of weapon to use, Alban and Horne shot the Iraqi, according to testimony at the recent hearing. Horne told investigators that he believed the Iraqi was alive after Alban's first shot, so he shot him as well.
The platoon leader, Lt. Erick Anderson, remains under investigation but has not been charged. At a recent hearing, Anderson refused to testify, invoking his right against self-incrimination.
Majid said his family received a total of $7,500 in compensation for the deaths of Hassan, another cousin and his brother.
Efforts to find Iraqi witnesses were made only after an attorney for Alban criticized the government at a hearing for failing to do enough to track down the victim's family.
"The witnesses should have the opportunity to have their day in court," said Capt. Catherine Robinson, a military attorney appointed to represent Alban.
"Those Iraqis were there," she said. "They were in the dump truck. They know what happened. They know what happened to their cousins, brothers and whoever else was there."
Government attorneys said the lack of records at the Iraqi police department and the dangerous conditions in Sadr City had hampered their investigation." There are security issues," said Capt. Emily Schiffer, chief of the legal unit that is pressing the case. "Also there are a lot of holes in the accountability" of the Iraqi police.
Investigators said the lack of a body or autopsy report could also hinder the investigation.
"If we don't have a body, we really don't have a case," Special Agent Herman Vanderhorst, the lead criminal investigator, testified.
Horne, who joined the Army in 1999, has been negotiating a plea bargain with military officials, attorneys said.
The initial attack by U.S. soldiers on the garbage truck is also under investigation to determine whether it was appropriate to open fire without warning. Military officials declined to provide details, saying an inquiry was underway.
Iraqis caught in the attack said they wanted an explanation.
"The Americans were acting like real cowboys," Raheem said. "I was just doing my job. There was nothing to suggest we were armed. Why did they open fire on us? I'm still waiting for an answer to that question."
Times special correspondent Raheem Salman contributed to this report.