Authorities are trying to convince jurors at Duncan's federal sentencing hearing that the convicted child molester should be executed for the kidnapping, torture and murder of 9-year-old Dylan Groene in 2005. Duncan has already been convicted in state court of murdering the boy's older brother, mother and stepfather at their Coeur d'Alene area home.
Testimony in the case was to resume Tuesday.
At Duncan's request, an attorney advising him asked U.S. District Judge Edward Lodge to bar the testimony about Sammiejo, Carmen and Anthony, saying it was irrelevant and prejudicial.
Since the jury only has the choice of imposing the death penalty or life without parole when it comes to sentencing Duncan, there's no likelihood he could prey on children in the future, the attorney, Mark Larranaga, said.
But Lodge sided with Assistant U.S. Attorney Wendy Olson, who argued the confessions to multiple murders show a lifelong pattern of violence.
"All of his crimes ... certainly illustrate that he could be a danger in the prison setting," Olson said.
Margaret Delaney, the mother of Sammiejo, 9, and Carmen, 11, sobbed frequently on the stand as she testified about the day her daughters disappeared.
Delaney said she left the two girls with their 15-year-old brother and another younger sibling with instructions to stay at a motel where they were staying. Then Delaney went to pick up a change of clothing for the children and to a friend's house where she could get money to buy some groceries.
While she was gone, the two girls decided to walk to a nearby fast food restaurant to see if they could get some food, Delaney said.
Their bodies were found months later in a suburban subdivision in Bothell, Wash. Duncan said he grabbed the girls on an impulse, and that he killed them by hitting them in the head with a crowbar, Sotka testified.
Anthony's stepfather, Ernesto Medina, told the jury about the day his 10-year-old boy disappeared, April 4, 1997. Medina said he was in his apartment with his wife, mother-in-law and 4-year-old daughter when he heard other children outside screaming "A man's got Tony! A man's got Tony!"
Medina called 911, then jumped in his car and began searching the neighborhood, thinking the abductor was on foot.
Vultures in a remote part of a canyon led authorities to the little boy's body, bound with duct tape and partially buried under a pile of rocks.
The boys who had been playing with Tony Martinez before his abduction reported that a man in a white car had offered them a dollar each to help him find his lost cat. After looking for a time they approached the car to get their money, and that's when the man grabbed Tony.
Sotka said Duncan told him he bludgeoned the boy with a rock that he found at the scene and wasn't sure whether the child was dead when he left him in the desert, but knew the wound was fatal. Duncan also said he taped the boy's mouth shut to stop him from crying out, because he'd been haunted by hearing Carmen scream "No!" after seeing her older sister murdered, Sotka said.
Authorities matched a partial fingerprint found on a roll of the duct tape near the body with Duncan's thumbprint, Richard Kinney, a fingerprint expert with the California attorney general's office, told the jury. Prosecutors in Riverside County have charged Duncan in Anthony's slaying and are seeking the death penalty.
King County sheriff's Sgt. John Urquhart said from Seattle on Monday that Duncan remains a "person of interest" in the murders of the two Seattle girls but has not been charged.
Of the seven people Duncan has acknowledged killing, only two are adults - the rest are between the ages of 9 and 13. All but one were bludgeoned to death. Dylan Groene was shot twice. Shasta Groene was rescued when Duncan was arrested in July 2005.
Associated Press writer Gene Johnson in Seattle contributed to this report.