Kootenai County Sheriff Department/AP
07/12/2005 AT 02:00 PM EDT
Convicted sex offender Joseph Edward Duncan III, who already faces kidnapping charges in the abduction of two children from a rural Idaho home, will be charged with three counts of first-degree murder, according to Kootenai County Prosecutor Bill Douglas, the Associated Press reports.
Duncan's charges "are for the premeditated murders of Brenda Groene, Slade Groene and Mark McKenzie," Douglas told TV reporters. The three were killed in their home around May 15, authorities say.
Shasta Groene, 8, and Dylan Groene, 9, were abducted from the home. A waitress at a Coeur d'Alene Denny's, recognizing the young girl from news reports, spotted Shasta with Duncan on July 2 and phoned 911. Duncan, 42, was arrested at the scene.
Dylan's body was found at a remote campsite in western Montana last week, after Shasta gave authorities information about where the children were held. Kootenai County officials have said they believe Duncan is the sole person responsible for the crimes.
Shasta Groene did not learn that Dylan was dead until last weekend, according to the children's father, Steve Groene, who was divorced from Brenda Groene. "She asked me last week in the hospital if I knew what had happened to Dylan," the elder Groene told The Spokesman-Review.
The public will be invited to a memorial service for Dylan in coming days, his father added.
Duncan, who was raised in Tacoma but had most recently lived in Fargo, N.D., is being held without bail in the Kootenai County Jail. He has already been charged with two counts of first-degree kidnapping in the case. The crime can bring the death penalty in Idaho.