BOISE, Idaho — Convicted sex offender Joseph Edward Duncan III, who beat a northern Idaho mother, her fiance and oldest son to death in 2005 before abducting her two youngest children, pleaded guilty to 10 federal counts Monday in the kidnapping and lengthy sexual abuse of the children and the murder of one of them.

Duncan, 44, faces a possible death penalty for the crimes, when a sentencing jury hears arguments scheduled for Jan. 28.

He told U.S. District Judge Edward Lodge that he has never tried to shun accountability for his actions.

“I just wanted to say that since my arrest I have never made any attempt to deny my responsibility,” he said, reading from a yellow legal tablet. “My plea today is not a confession in the sense that I already confessed … I will continue to accept that responsibility to the death.”

Assistant U.S. Attorney Tracy Whelan told the court that Duncan held 8-year-old Shasta Groene and her 9-year-old brother, Dylan, at a remote Montana campsite, sexually abusing them for nearly two months and threatening them with death if they disobeyed him. Whelan said Duncan used recording and computer equipment to videotape the abuse of Dylan before shooting the child to death with a sawed-off .12 gauge shotgun.

Duncan did not make a plea deal. He faces a possible death penalty on three of the felonies: kidnapping resulting in death, sexual exploitation of a child resulting in death, and using a firearm during and in relation to a crime of violence resulting in death.

He also pleaded guilty to kidnapping, two counts of aggravated sexual abuse of a minor, being a felon in possession of a firearm, transportation of a stolen firearm, possession of an unregistered firearm, and transportation of a stolen vehicle.

Duncan’s plea means that Shasta, now 11 and the only survivor of the attack on her family, will be spared the trauma of testifying at his trial. It was not clear if she will be expected to give a victim impact statement for a federal sentencing jury.

Duncan also has been charged in California with the 1997 slaying of 10-year-old Anthony Martinez in Indio, Calif. Prosecutors there have said they intend to seek the death penalty. In addition, he is a suspect in the 1996 Seattle-area killings of 9-year-old Carmen Cubias and 11-year-old Sammiejo White.

Neither Shasta, nor her father, Steve Groene, attended Monday’s hearing. Steve Groene, reached by telephone in Coeur d’Alene, was relieved by the news.

“For my family, we’re happy,” Groene said. “She (Shasta) does not have to testify in this phase of this.”

Shasta was at school Monday and Groene said he would tell her of Duncan’s plea later in the day. He declined additional comment, citing a gag order that Lodge issued for all parties.

Lodge did not consider a media request Monday to lift or modify the gag order. Attorneys on both sides declined to comment because of it.

Duncan is a Tacoma native who spent most of his adult life in Washington state prisons for sexual crimes against children.

Court documents say he was on the run from a child molestation charge in Minnesota in May 2005 when he drove past the Groene home on I-90 east of Coeur d’Alene, spotting Shasta, then 8, and her 9-year-old brother, Dylan, playing outside. Duncan stalked the Groene family for several days before attacking the family.

In his plea, Duncan admitted kidnapping Shasta and Dylan from the home and driving them into the mountains near St. Regis, Mont., where he sexually abused them for weeks before killing Dylan. The boy’s body was found at a remote campsite.