Dr. Sharon Cooper's testimony in U.S. District Court followed the presentation of a taped interview in which Shasta Groene, 8 at the time, related grim details of Duncan's sexual abuse and slaying of her older brother, Dylan. Groene, who also said she was sexually abuse and tortured, told the jury Duncan accidentally shot her brother in the stomach with a shotgun and then blasted him in the head after deciding the boy's life couldn't be saved.
Cooper said the description of the boy's injury - he was eviscerated, his sister said, with his "guts" hanging out - indicated it was "a very potentially salvageable injury."
"We see this on the battlefield fairly often," Cooper told the jury. "They can live for several hours like that."
Cooper also said Duncan may have had enough time to get Dylan Groene to a hospital from the remote western Montana campsite where the shooting occurred.
While in the Army, Cooper was assigned to child abuse cases on military installations in Hawaii and the Pacific Rim before becoming chief of pediatrics at Fort Bragg, N.C. She said she performed a medical assessment of Shasta Groene after her rescue, interviewed her father, Steve Groene, and reviewed interviews of the girl by law enforcement officers.
Duncan pleaded guilty in December to 10 federal counts in the 2005 kidnapping of the Coeur d'Alene-area children and the murder of the boy. A jury must decide whether Duncan should be executed or spend life in prison without parole.
Duncan, acting as his own attorney in the sentencing phase, suggested in cross-examining Cooper that the girl was exaggerating her brother's injury.
"How much in your experience do children tend to elaborate or exaggerate and fill in details ... especially after a traumatic experience like that?" Duncan asked.
Children who exaggerate are typically much younger, between 4 and 6, and lack the vocabulary to describe what happened to them, Cooper said.
Duncan asked whether the "guts" mentioned by the girl could have been RamDon noodles the boy had eaten earlier.
Cooper said that was unlikely because chewed-up noodles wouldn't look like intestines. Besides, she told the jury, food would spill out of an abdominal wound only if the stomach also had been pierced.
Later in the morning, FBI Agent Mike Stoke told the jury he found a piece of Dylan Groene's skull at the campsite. Some jurors covered their mouths and looked down as the fragment, contained in a plastic evidence envelope, was displayed in court.
In opening statements last week, U.S. Attorney Tom Moss told the jury that the skull fragment was the only part of the boy's remains that were found at the campsite that was intact enough to yield results in a DNA test.
Jurors also were told by FBI firearms expert John Web that he could not get the shotgun with which the boy was shot to fire accidentally in "drop tests." Web added that the shotgun required five pounds of pressure on the trigger to fire.
Duncan bludgeoned to death the children's older brother, mother and her fiance at their home before abducting the pair in May 2005, setting off a nationwide manhunt. Duncan has pleaded guilty in state court to the killings at the house.
While it is The Associated Press' policy not to identify victims of sexual assault in most cases, the search for Shasta and Dylan Groene was so heavily publicized that their names are widely known.
Duncan, formerly from Tacoma, Wash., has a long string of arrests and convictions for crimes ranging from car theft to rape and molestation. He is suspected in the slayings of two half-sisters from Seattle in 1996 and is charged with killing a young boy in Riverside County, Calif., in 1997.