Joseph Edward Duncan III, facing the death penalty for the 2005 kidnapping of two northern Idaho children and the murder of one of them, wrote a letter to his mother blaming society for feeding the evil in his heart, a prosecution witness testified Friday.

Duncan, a convicted pedophile from Tacoma, Wash., pleaded guilty in December to 10 federal charges related to the kidnapping of young Shasta Groene and her brother Dylan. A U.S. District Court jury is hearing testimony on whether he should be sentenced to death or life in prison without parole on three of the counts.

The children were taken from their Coeur d'Alene home in May 2005 after Duncan fatally bludgeoned the children's mother, Brenda Groene, their 13-year-old brother Slade, and the mother's fiance, Mark McKenzie.

Both children were sexually abused before Duncan shot and killed 9-year-old Dylan at a Montana campsite. Shasta, then 8, was rescued July 2, 2005, when a waitress spotted her and Duncan in a Coeur d'Alene restaurant.

Duncan earlier pleaded guilty in state court to killing McKenzie and Slade and Brenda Groene. Sentencing on those charges is not at issue here.

Friday morning, Assistant U.S. Attorney Wendy Olson asked Idaho State Police Detective Fred Swanson to read a letter written by Duncan to his mother. The letter, apparently never sent, was found folded in Duncan's coat pocket.

In it, Duncan laments his struggles with God and says he wishes he could kill himself but his will to live is too strong.

"I have once again become a medium of violence in the world," he wrote.

There is "love in my heart and yet at the same time there is a huge reservoir of hatred (evil). ... I am driven by my hatred for our society ('the system') while at the same time tortured by my own compassion. ... I don't know what God wants for me, I just don't know."

Duncan's letter complained that he had been taken over by a demon.

"God has shown me the face of evil," he wrote in the letter. "Evil is real only because we make it real. ... Evil can live in a person and society as well. ... I have been inflicted by an evil 'demon' that is nurtured by our so-called Criminal Justice System .... But know I'm still fighting" and asking God to guide him, Duncan wrote.

Admitted into evidence Friday were weapons, tools, computer equipment and camping gear, including what Swanson said was a sawed-off shotgun believed to have been used to kill Dylan. Swanson said a large tree saw, a hack saw, a survival knife, padlocks, binoculars, a hatchet and night vision goggles also were found in Duncan's stolen Jeep Grand Cherokee.

A laptop computer was plugged into the dashboard, and a video camera, digital camera, a microdrive and other equipment were in the car, he said.

Computer experts were able to pull some video and other images off of the microdrive, but failed to crack Duncan's encrypted computer password despite hundreds of attempts, FBI computer forensic examiner Loren Mercer testified.

Duncan, who is representing himself, appeared to nod off at times during Friday morning's testimony. At one point a snoring noise was picked up by the courtroom's sound system.

Duncan has a long string of arrests and prison time for crimes ranging from car theft to rape and molestation. He is suspected in the 1996 slayings of two half-sisters from Seattle and is charged with the 1997 killing of a young boy in Riverside County, Calif.