Lawyers for a man accused of killing three members of a family so he could molest two children said a prosecutor rejected Joseph Edward Duncan III's offer to confess in exchange for being spared the death penalty.

In a letter to Prosecutor Bill Douglas of Kootenai County, Idaho, Duncan's lawyers John Adams and Roger Peven said their client will cooperate fully with law enforcement if granted a deal, even though he could face a death sentence in federal court later.

Peven, head of the federal public defender's office in Spokane, said Douglas has rejected the offer.

Douglas has consistently rejected a plea bargain for Duncan. A spokeswoman in his office said he did not want to comment because jury selection in the case begins Monday.

Duncan is accused of killing the mother of Dylan and Shasta Groene, their 13-year old brother and their mother's boyfriend in May 2005 at their home near Coeur d'Alene, Idaho.

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He is suspected of taking Dylan and Shasta to a campsite in Montana, and Dylan, 9, was killed at some point. Shasta, now 9, was rescued at a Denny's restaurant in Coeur d'Alene after seven weeks of captivity.

"Mr. Duncan will admit to the intentional killing of Dylan Groene in Montana in the early part of 2005, as well as all other crimes committed against Shasta and Dylan Groene," said the letter, dated Oct. 4.

Duncan's trial in the three Idaho killings is to begin Monday in Coeur d'Alene.

Court documents allege Duncan, who spent most of his adult life in Washington prisons for sexual crimes against children, committed the slayings so he could kidnap the two children for sex.

Peven said Duncan is willing to plead guilty to spare Shasta Groene the trauma of having to testify in court against him.

Steve Groene, father of the abducted children, in recent months has asked for a plea bargain so Shasta would not have to face Duncan in court. Steve Groene is recovering from recent throat cancer surgery and was not immediately available for comment Wednesday.

Shasta is scheduled to meet with a judge on Thursday in a closed session to determine if she is competent to testify because of her age, and also whether she will be given special considerations such as not having to look directly at Duncan, or having a comforting person sit near her.

Duncan understood that making the confessions would have made it easier for the federal government to convict him of expected charges of kidnapping and murder in the abduction of Shasta and Dylan when the state case concludes, Peven said.

At the time of his arrest last year, Duncan was on the run from a molestation charge in Minnesota. Duncan has also been implicated in the deaths of two children in the Seattle area and one child in Southern California.

Peven said he did not believe Duncan was involved in the killing of any other children.

The letter said that in exchange for a sentence of life in prison without parole, Duncan would plead guilty to first-degree murder and first-degree kidnapping in the cases involving Brenda Groene; her fiance, Mark McKenzie; and Groene's son Slade.

He also agreed to give law enforcers access to his encrypted computer files, according to the letter. A computer expert, Duncan has bragged that officers wouldn't be able to crack into his computer files — thought to contain details of criminal activities — for 30 years.