Last Updated 8:50 p.m. ET
GRAHAM, Wash. - A house explosion has killed Josh Powell, the husband of missing Utah woman Susan Powell, and their two sons.
The three were killed Sunday afternoon in a house explosion at a residence belonging to Powell, who has been a person of interest in the disappearance of his wife since she vanished in December 2009.
CBS Affiliate KIRO reports that Powell had a supervised visit Sunday with his sons, who had been placed in custody of Susan's parents.
Graham Fire and Rescue Chief Gary Franz told The Associated Press that the explosion occurred moments after a Child Protective Services worker brought the two boys to the home for a supervised visit. He said 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.
"Everything we know right now, this has become a crime scene," Franz said.
Sgt. Ed Troyer, Pierce County sheriff's spokesman, said emails that Powell sent authorities seemed to confirm that Powell planned the deadly blast. Troyer didn't elaborate on the contents of the emails, but said they make police believe "this is intentional, this is planned."
Authorities said they found three bodies in the home late Sunday afternoon as fire crews and police continued to search the rubble. Troyer said it appeared some sort of accelerant was used to make the house burn faster.
Jeffrey Bassett, who represented Powell in the custody case, said he received a brief email from his client just minutes before Powell and the two boys died. It said, "I'm sorry, goodbye."
The email arrived at 12:05 p.m. Sunday, about 10 minutes before the explosion, but he didn't see it until two hours later, when others told him Josh and the boys had been killed. He said he knew Josh was upset after being ordered to undergo a psycho-sexual evaluation recently, but he didn't see this coming.
Powell was under investigation in the disappearance of his 28-year-old wife from their West Valley City, Utah. He claimed he had taken the boys on a midnight excursion in freezing temperatures when she vanished.
In August 2011 Powell told CBS' "The Early Show" that he had nothing to do with her disappearance, and did not kill her. "I would never even hurt her. People who know me know that I could never hurt Susan."
The case took a bizarre turn last year after Powell's father, Steve, was arrested for investigation of voyeurism and possessing child pornography. Josh was living at his father's home at the time. Last September a judge granted temporary custody of the two children to their maternal grandparents.
Last week a judge denied Powell custody of his two children, and said they would remain in the custody of Susan's parents owing to new allegations that sexually explicit images were found on a home computer belonging to Powell.
The judge cited allegations last September against Josh's father in her decision.
The next custody hearing was set for July.
Lawyer Steve Downing, who represented Susan Powell's parents, Chuck and Judy Cox, in the custody fight, said: "It's the most horrifying thing you can imagine happening ...The Coxes are absolutely devastated. They were always very fearful of him doing something like this, and he did it."
Bassett said he represented Powell free of charge because "every parent deserves the right to an attorney." Powell called or emailed him at least once a day, and often more than that, and in their conversations "he never once admitted doing anything regarding Susan. In fact, he denied it."
Sgt. Mike Powell of the West Valley City Police Department in Utah, which is handling the investigation into Susan Powell's disappearance, said it was too soon to say how Josh Powell's death may impact their probe.
"Quite frankly, this has obviously quickly unfolded up in Washington and we're obviously just working through the details ourselves here," said Powell, who is not related to the family.
Kirk Graves, 39, of West Jordan, Utah, whose wife is Josh Powell's brother-in-law, said they were stunned by the news.
"We never contemplated the idea he would do something like this. You just don't expect it from a father," he said. "His world was falling apart around him and he was going to lose his boys and get arrested for Susan's disappearance. He's a narcissist and he has no love for anyone but himself.
The day of the hearing last Wednesday, Josh Powell submitted a six-page affidavit attesting to his love of the boys and his competence as a caregiver and insisting that it was time for the boys to come home.
"For over four months already, my interactions with my sons and many other aspects of my character have been investigated and documented by CPS," he wrote. "I have proven myself as a fit and loving father who provides a stable home even in the face of great adversity. ... It is time for my sons to come home."