A former US soldier has been found guilty of the rape and murder of a 14-year-old Iraqi girl and of then killing her parents and sister.

Steven Dale Green was convicted by a civilian court in the US state of Kentucky on Thursday and faces a possible death sentence over the crimes.

He was found guilty of 17 criminal charges including rape, murder and obstruction of justice.

Green was discharged from the army due to a "personality disorder" before his role in the murders was suspected.

His defence team had asked the jury to consider the "context" of war, saying soldiers lacked leadership and received little help from the military to deal with the loss of friends in combat.

Premeditated attack

Marisa Ford, a prosecution lawyer, said the losses suffered by Green's unit did not excuse the rape of Abeer al-Janabi and the murders of her and her family in their home south of Baghdad on March 12, 2006.

"The evidence in this case suggests the defendant was acting purposefully and intentionally with full knowledge of what he was doing," Ford said.

James Barker and Paul Cortez, two other soldiers who are serving 100 and 90 years for their role in the brutal attack, testified against Green during the trial.

Green and other soldiers changed their clothes and disguised their appearance to throw suspicion on Iraqi fighters, Ford said.

They then burned Abeer's body to hide evidence and burned their own clothes to destroy anything that might link them to the crime, she said.

"This was a planned, premeditated crime which was carried out in cold blood," Ford said.