The case of missing Utah mother Susan Powell took a horrific turn Sunday in Washington State.
Officials say her husband, who was a person of interest in that case, killed their two children and himself.
Home video shot minutes after firefighters arrived on the scene shows Josh Powell's home engulfed in flames.
"I just heard a huge explosion," neighbor Ryan Mickle says. "It shook my house and then I ran outside and the whole house was on fire almost immediately."
Inside, officials found the bodies of Powell and his two young sons, seven-year-old Charles and five-year-old Braden.
"This wasn't an accident," Ed Troyer, of the Pierce County Sheriff's Department, declared. "This was Josh Powell, who we believe killed his kids and himself ... dead in the fire."
About ten minutes before the fire started, Powell reportedly sent his attorney an email that read, "I'm sorry. Goodbye." Then, just minutes after his children were dropped off by a social worker for a supervised visit, the explosion occurred.
"He grabbed the kids," said Troyer, "locked her out of the house, and immediately, the house went up in flames. ... We believe that the house fire went up so fast that accelerants were used."
Powell was involved in a bitter custody battle with his children's' grandparents. Last week, a Washington judge denied Powell custody of his two sons and ordered him to undergo a psycho-sexual evaluation after child pornography was found on his father's computer.
Powell's fitness as a father has been under scrutiny since the mysterious disappearance of his wife, Susan Cox Powell, from their Utah home in December, 2009. Powell told investigators that, on the night his wife went missing, he had taken his sons camping in a blizzard to a remote part of the state.
In an interview with CBS News, Powell denied having any involvement in her disappearance. Asked directly whether he killed Susan Powell, Josh Powell replied, "I've never even hurt her. People who know me know that I could never hurt Susan."
But an attorney for the Cox family says the kids had recently started to open up about what happened on the night of their mother's disappearance. Steve Downing said, "They had gone camping. Their mother had been in the trunk and later, their mom and dad walked out into the desert and mommy got lost."
At Charlie and Braden's school, students and parents gathered for a candlelight vigil.
And while investigators piece together what happened in Washington, police in Utah will be taking a fresh look at Susan Cox Powell's disappearance and Josh Powell's involvement.
"This is a terrible act of murder involving two young children," says Pierce County Sheriff Paul Pastor. "Let's call it like it is. Let's call it a horrible murder, because that's exactly what we have here."
To see Ben Tracy's report, click on the video in the player above. For insight from "CBS This Morning" senior correspondent John Miller, click on the video below: