KAMLOOPS, B.C. - A little girl found slain with her two younger brothers fought back but also pleaded for forgiveness as she was slashed to death, the killer - her father - told a B.C. court on Wednesday.

Allan Schoenborn sobbed in the witness box at his murder trial, where he described killing 10-year-old Kaitlynne, eight-year-old Cordon and five-year-old Max.

The 41-year-old vividly recounted for a B.C. Supreme Court judge how he swung a cleaver at Kaitlynne's neck.

He told the court that the girl fought back, putting her hand up and crying out "I'm sorry, Daddy, I'm sorry," and then pulled his hair as he slashed her neck.

"I told her to go to the white father," he testified.

Schoenborn is on trial for three counts of first-degree murder.

The defence is arguing that Schoenborn should be found not criminally responsible for the killings due to mental disorder, but the Crown contends the killings were an act of revenge against the children's mother.

Schoenborn said he and the children had had a good and happy day flying kites together, but he became convinced that the trio was being molested. After putting them to bed, he said he realized he had no choice but to kill them all because no one - including his wife who he had just phoned - would help.

"Do I walk away if my kids are being molested? Do I look them in the eye again?" he asked through sobs.

He said he couldn't let the children endure being molested.

The 41-year-old shook and cried as he described how he separated the sleeping children before killing them one at a time.

Schoenborn said he killed Cordon next, suffocating the boy with a pillow.

"I thought it was going to be quick with Kaitlynne," he told the judge, who is hearing the case without a jury.

But it wasn't quick, he said, so he suffocated the boys instead.

Schoenborn said he used a yellow plastic bag to suffocate Max, which was also tougher than he expected.

"I told him to just go to that light," he said.

He said he then wrote "forever young" on the walls with soy sauce, and "gone to Neverland" in blood on pillows because he wanted the message to be seen by his wife, and feared if he left a letter someone else would find it and take it.

Schoenborn said he tried to kill himself at home, but failed and instead ran to the mountains where he again tried to commit suicide. He was discovered wandering in the woods 10 days later, dehydrated and suffering self-inflicted wounds.

The accused man said he killed his children "for all the right reasons, I did it for them, my children."

"I gave my children up to be in a better place," he told the judge, who is hearing the case without a jury.

The children's bodies were found by their mother in their Merritt, B.C., home on April 6, 2008. Their mother, Darcie Clarke, earlier testified that she left them in Schoenborn's care and stayed at her mother's that weekend.

Schoenborn was asked by his lawyer if it was true, as Clarke said in her testimony, that he sometimes heard voices.

"I don't know how I was hearing them but I know I was hearing them," he said. "I'm hearing and thinking it's inside me ... it's in my nasal or in my mouth. ... They say derogatory things to me that no one else can hear."

He testified that in the days prior to the slayings he believed there was a conspiracy to keep his family apart being perpetrated by a government ministry, the police and the school board.

Schoenborn recounted a history of being admitted to psychiatric wards of hospitals.

He also told the judge that he adored his wife but believed she had cheated on him with at least three different men.

Schoenborn has acted bizarrely in court, shouting questions at witnesses and other verbal outbursts from the prisoner's box. But when he wasn't crying he remained calm and attentive to his lawyer's questions.

Schoenborn will return to the witness stand on Thursday.

While in the witness box, he said he believes his children have forgiven him. He said as he sat in the prison courtyard once, he saw sparkles on some water and had a vision of his daughter coming to him and forgiving him.

"If Kaitlynne forgives me, I know the boys forgive me because I was a little rougher on Kaitlynne," he told the judge while quietly weeping.