The court trying Saddam Hussein has heard graphic accounts of how hundreds of Kurdish women and children were killed and buried in mass graves.
Saddam Hussein said the US expert's testimony was unreliable
US forensics expert Michael Trimble said three graves containing corpses of victims killed in the so-called Anfal campaign in 1988 had been uncovered.
Mr Trimble said the victims had been killed in a "highly organised programme of execution".
Saddam Hussein was sentenced to death earlier this month after another trial.
The former Iraqi leader and his six co-defendants have pleaded innocent to charges of war crimes and crimes against humanity in connection with the Anfal campaign in which at least 100,000 people were killed.
Saddam Hussein and his cousin, Ali Hassan al-Majid, also face charges of genocide.
'Bound and blindfolded'
Mr Trimble, who heads the Mass Graves Investigation Team, said of the 301 bodies found, 183 belonged to children.
He said 90% of the children were under 13 years old.
"The captives were often bound and blindfolded. The captives were led into the grave and then executed with pistols or automatic assault rifle fire. The graves were then covered by those directing the execution."
In some of the most harrowing evidence presented so far to the court, Mr Trimble described how children died in their mothers' arms.
He showed the court slides of a child whose legs were cut in half by a bullet. Another child had wounds to the front and back.
"It is very clear these people were twisting as they were getting shot at," said Mr Trimble.
"There is a terror that takes over as people try to get out of the way. It's a very common human response."
He said a pregnant woman and her unborn child had been killed by a single shot, while another child who had not been shot had probably been smothered to death by a corpse.
Saddam Hussein dismissed the testimony, saying Mr Trimble could not be trusted.
"Let me suggest the court consider what is said by the American expert but also call a new trial expert that has nothing to do with the enemy or the army of the enemy," he said.
The trial was adjourned until Monday.