US soldiers have had to answer a number of accusations of abuse
A US soldier has been convicted of murder for his involvement in the killing of four Iraqis who were shot and dumped in a Baghdad canal in 2007.
Sgt Michael Leahy Jr had confessed to investigators that he shot an Iraqi in the back of the head from close range.
His lawyers argued that the stress of being in a conflict zone for so long meant he was unable to reason properly.
But a panel at a court martial in Vilseck, Germany, dismissed the claims and will decide Leahy's sentence later.
The 28-year-old army medic, from Lockport, Illinois, faces a maximum life term in jail and a dishonourable discharge from the army.
'Fear and madness'
The victims were a group of Iraqis who were detained briefly and questioned over an attack on a Baghdad military base.
Leahy was one of a group of soldiers who took detainees away after it was decided there was not enough evidence to charge them.
Blindfolded and gagged, the four were then shot and dumped in a canal.
During interrogation in January 2008, Leahy told military investigators he had shot an Iraqi in the back of the head with a pistol.
The Associated Press reported that a video of the questioning was played at his court-martial hearing in the US army's Rose Barracks earlier this week.
"The detainee I shot fell back on me," he was heard to say in the videotape.
His lawyer, Frank Spinner, argued that Leahy went along with the killings because he was dazed from a lack of sleep.
"The tragedy resulted not so much by design but rather the working of fear, danger and madness attendant on many combat operations," Mr Spinner said in his closing arguments.
But prosecuting lawyer Cpt Derrick Grace said the soldiers could not be allowed to claim that they were protecting themselves "from future harm".
Leahy was found guilty of murder and conspiracy to commit murder by the nine-person panel.
Several other soldiers also face charges for involvement in the same incident.