The lawyer for Susan Cox Powell's parents says the children had started talking to their grandparents about things they remembered from the night their mother vanished.

"They were beginning to verbalize more," said attorney Steve Downing, whose clients, the parents of Susan Powell, Chuck and Judy Cox, had custody of the children. "The oldest boy talked about that they went camping and that Mommy was in the trunk. Mom and Dad got out of the car and Mom disappeared."

Susan Cox Powell's two children died along with their father on Sunday after police say he ignited his home.

The explosion occurred moments after a social worker brought the two boys, 5-year-old Braden and 7-year-old Charles, to the home for a supervised visit, said Graham Fire and Rescue Chief Gary Franz.

Powell let the boys in the house, then blocked the social worker from entering. The social worker called her supervisors to report that she could smell gas, and the home exploded.

"It's the most horrifying thing you can imagine happening," said Downing, who represented Chuck and Judy Cox, in the custody fight. "The Coxes are absolutely devastated. They were always very fearful of him doing something like this, and he did it."

Seattle Attorney Anne Bremner, who represented Chuck and Judy Cox in the civil case involving the disappearance of their daughter, said she'd heard the Powell children had begun speaking about their mother around Christmas.

"It's clear that there was an indication at least to Josh that he was looking at some real witnesses," said Bremner. "He would say things like, 'They're trying to turn the boys against me,' [...] "When in reality, it's clear that his fear was really the opposite: What were the boys saying?"

Listen to Attorney Anne Bremner on Josh Powell taking his kids lives

Pierce County Sheriff's spokesman Ed Troyer said they believe the fire was set intentionally.

"We're looking at this as a straight up double homicide of the two children, that he [Josh Powell] is the one who did it. He planned it out, and he did it," said Troyer, in an appearance on 97.3 KIRO FM Seattle's Morning News.

Listen to Pierce County Detective Sergeant Ed Troyer

The two boys had been in the custody of their grandparents since Josh Powell's father Steven Powell was arrested for investigation of voyeurism and possessing child pornography. Josh was living at his father's home at the time, and a judge gave Susan Powell's parents custody of the boys.

As devastated as Susan's parents are to have lost her and now her sons, they aren't critical of how the custody case was handled, said Downing.

"They knew that legally, he would probably have supervised visitation," Downing said. "It was their belief he had something to do with Susan's disappearance, and that ultimately, he could harm the children. But they believed the state had listened to them and had taken appropriate measures to protect them. They don't know what more the state could have done."

Sherry Hill, a spokeswoman for the Washington state Department of Social and Health Services, said the social worker who was with the children Sunday was not a Child Protective Services employee but a contract worker with a private agency that supervises visits for the state.

Troyer said the woman was "traumatized" by Sunday's events.

"She did everything she could," said Troyer. "It wasn't for lack of her trying to do what she could to prevent this. It's just with Josh setting this up, having pre-knowledge of this is what he's going to do. It doesn't matter who would have had these kids over here, this was going to happen."

Troyer said investigators will be on the scene Monday trying to get more details of the logistics of the crime.

The Washington Department of Social and Health Services will also conduct a formal child fatality review.

The Associated Press contributed to this report.

97.3 KIRO FM Staff, Staff report

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