Duncan, 58, had been diagnosed with terminal brain cancer before his death.
Duncan tortured both children and killed the boy. The boy’s sister, Shasta Groene, was spotted several weeks later in a restaurant in Coeur d’Alene and Duncan was arrested, the release said.
Duncan also admitted to killing other children, the release said.
Anthony was playing in a neighbor’s yard in April 1997 with his brother and some friends when Duncan abducted him, according to the district attorney’s office release. Duncan had first tried to grab the boy’s brother, and as Anthony tried to intervene, Duncan grabbed him, forced him into a car and drove away, the release said.
The child’s body was found about two weeks later, the release said.
Duncan had been in custody on death row at the Terra Haute Federal Correctional Institution in Indiana.