(CNN)Serial killer Joseph Edward Duncan III, who was facing execution after being convicted for the 2005 kidnapping and killing of Dylan Groene, a 9-year-old Idaho boy, died Sunday morning, according to a news release from the United States Attorney's Office for the District of Idaho.
Serial killer Joseph Edward Duncan dies
Duncan, 58, had been diagnosed with terminal brain cancer before his death.
In May 2005, Duncan murdered Brenda Groene, the boy's mother; Slade Groene, the boy's teenage brother; and Mark McKenzie, the mother's boyfriend at their home just outside Coeur d'Alene, Idaho, before kidnapping the boy and his 8-year-old sister, according to release.
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.
"This crime was horrendous and its impact on the families, the community, the jurors, court staff, our litigation team, and law enforcement were far reaching," Acting US Attorney Rafael M. Gonzalez Jr. said in a statement. "While his death will not bring back the lives cut so tragically short or remove the indelible memories of his unspeakable acts, perhaps death will now allow space for some degree of healing, peace and closure."
Duncan also admitted to killing other children, the release said.
Among them was Anthony Martinez, 10, in Beaumont, California, the Riverside County District Attorney's office said in a separate news release.
"The sun is brighter today, and my soul is lighter," Anthony's mother, Diana, said in a statement. "The world is a more beautiful place without the evil that is Joseph Duncan. God chose to make his end a long suffering and I believe that is fitting. The horror of his thoughts consumed him."
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.
"While I would've liked to witness his execution, knowing he is now standing before God being held accountable for what he has done, what he did to my son, and the horrible crimes he committed to others, that's the real justice," Anthony's father, Ernesto, said in a statement.
Duncan had been in custody on death row at the Terra Haute Federal Correctional Institution in Indiana.