A US army captain charged with the murder of an Iraqi militant said the man was killed out of mercy, a US military hearing has been told.
The shooting happened near the Iraqi city of Kufa
A colleague told the hearing in Germany that Capt Rogelio Maynulet, 29, shot the man in the head as "there was nothing more that could be done".
Capt Maynulet faces life in prison if guilty of murdering Karim Hassan, 36.
The hearing viewed footage of the killing caught by a US military drone aircraft, the AP news agency said.
Reporters were asked to leave the room while the video was shown to an expert witness in neurosurgery, lest it should give away secrets of US technology in Iraq.
The death occurred on 21 May near the central Iraqi
town of Kufa.
US troops fired at a vehicle they thought was carrying militants linked to the radical Shia cleric Moqtada Sadr.
The hearing was told that the car's passenger was killed immediately, while the driver was badly injured.
Lt Colin Cremin testified that Capt Maynulet and others in his unit had described the incident to him, saying the driver "had half his brain hanging out, there was nothing more that could be done for him."
Capt Maynulet had confirmed he had shot the man in the base of the neck or the back of the head, he said.
"It was something he didn't want to do but it was the
compassionate response, it was definitely the humane response," he said.
Various witnesses praised Capt Maynulet.
The prosecution alleges he broke US rules
of engagement and used illegal weapons.
His lawyer, Capt William Helixon, said later:
"The individual was neither a prisoner nor a civilian but an
Iraqi insurgent characterised by the [US] government as an enemy
Mr Hassan's family does not deny that he was working for Mr Sadr.
Capt Maynulet has denied charges of murder and dereliction of duty.
The hearing has been held to decide whether the case should go to a full court martial.