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00:10 - Source: CNN

Check out CNN affiliates KCPQ, KIRO, KOMO, KUTV and KSTU for more on the story. Tune in to HLN’s “Nancy Grace” at 8 and 10 p.m. ET Monday for an interview with Denise Cox, Susan Cox-Powell’s sister.

Story highlights

NEW: Powell kids had chop wounds, autopsy shows

Josh Powell and his sons died of carbon monoxide poisoning

Powell sent goodbye e-mails to his pastor, others just minutes before the fire

A Utah police chief vows to keep on the case of Susan Cox-Powell's disappearance

Puyallup, Washington CNN  — 

The two sons of a Washington man killed along with their father in a weekend fire suffered hatchet wounds before dying of carbon monoxide poisoning, authorities said Monday.

Investigators found the hatchet they believe was used on the boys in Powell’s home, said Troyer. Authorities believe Powell set an explosive fire there after wounding the boys Sunday afternoon.

Autopsies showed his sons suffered “chop” injuries to their necks, but both boys and their father died from inhaling carbon monoxide, the county medical examiner’s office said.

Powell’s death was ruled a suicide, while his sons’ deaths were determined to be homicides. Powell first gave toys and books to charity, sent multiple goodbye e-mails and doused the Puyallup, Washington, home with gasoline before setting it ablaze, authorities said Monday.

That evidence suggests that Josh Powell planned a murder-suicide for some time, Troyer said.

“He was making arrangement to leave this place, so he had some knowledge of what he was going to do,” he told CNN’s John King. “(I) believe this was intentional – it’s two counts of murder and then suicide.”

The saga began two years ago in the Salt Lake City suburb of West Valley City, Utah, when 28-year-old Cox-Powell disappeared.

Nancy Grace interviews Susan Cox-Powell’s sister

Before he set fire to his home, Powell sent his attorney an e-mail saying simply: “I’m sorry. Goodbye.”

He also sent e-mails to his pastor and others just minutes before the fire, giving instructions on how to handle his end-of-life business, according to Troyer. Powell donated his sons’ toys and books to a local charity, seemingly to clean house, he said.

The spokesman added that authorities found two five-gallon cans of gas in the home, one of which appeared to have been lit right next to the bodies, which were found together in the same room.

The sheriff’s department has copies of an e-mail Powell sent to his attorney as well as family and friends that said “he couldn’t live with what was going on,” Troyer said.

The deaths of Powell and the children could mean Cox-Powell’s disappearance might never be solved.

Still, the case remains open and investigators vowed to pursue it until the point of closure.

Follow a timeline of the case

“I promised the Coxes I wasn’t giving up, and I’m still not because we want to get some closure here,” West Valley City, Utah, Police Chief Buzz Nielsen said Monday. “The case is still active; we’re not closing the case. We still got things that have not been resolved.”

“The case is still active; we’re not closing the case. We still got things that have not been resolved,” he said.

Powell, who was never charged in his wife’s disappearance, was embroiled in a bitter custody dispute with her parents.

“Words can’t describe any of this … I can’t imagine any of us going through what Chuck and Judy Cox have gone through, losing their daughter and losing these dear little boys,” attorney Anne Bremner, who represented Charles and Judith Cox in the disappearance of their daughter, told HLN’s Vinnie Politan.

The children, at least the older boy, Charlie, had reached the age where they may have been giving away information, Bremner said.

“I know that to be true in this case because as recently as Christmas, the boys told their grandparents, ‘Mommy’s in the mine. If we go to the mine, we’ll find Mommy,’” she said.

Authorities have searched mines in Utah and Nevada for Cox-Powell, Bremner said.

When asked Monday whether she feared Powell would ever hurt his children, Cox-Powell’s sister, Denise Cox, responded: “Absolutely.”

“From the get go, from when he was named a person of interest, the boys should have been taken away from him, and he should not have been allowed visitation,” she told HLN’s Nancy Grace.

The children had started “opening up and talking to my parents about what happened that night,” in recent months, she said.

“The boys really, once they started opening up to our family, they started closing down on their dad,” the sister told HLN.

According to investigators, Powell had said the last time he saw his wife was the night he and his sons – then ages 2 and 4 – left to go camping after midnight in freezing weather.

Cox-Powell’s sister eventually reported her missing. A month later, Powell and his children moved from Utah to Washington.

As late as last month, Utah authorities were still working to connect Powell to the disappearance of his wife, who authorities believe is dead.

The double homicide and suicide on Sunday came days after a judge refused Powell’s petition to regain custody of his children. The judge instead ordered Powell undergo psychological evaluations – an order that came after authorities turned up child pornography in the home Powell shared with his father, Steven Powell.

As part of the investigation into Cox-Powell’s disappearance, Utah authorities searched the Washington house where Powell, his two sons and his father, Steven Powell, were living last year.

During the search, investigators “discovered numerous images and recordings of adult and juvenile females,” according to a statement released by the Pierce County sheriff’s department.