Graham, Wash. • A beleaguered Josh Powell — under suspicion for the 2009 disappearance of his wife and fighting an uphill battle for custody of his two young boys — killed himself and his sons on Sunday by setting fire to his Washington state home, officials said.

Calling it a "double murder/suicide," authorities said late Sunday the blaze that leveled Powell’s Graham home was "very well-planned" and was fueled by accelerants spread throughout the residence.

"Everything that happened was intentional," said Ed Troyer of the Pierce County Sheriff’s Office.

The fire broke out about 12:30 p.m., Washington time, just moments after a social worker had arrived with the boys — 7-year-old Charlie and 5-year-old Braden — for a supervised visit with their father.

When the boys entered the home, Josh Powell locked out the social worker, who pounded on the door and a window, then tried to call Josh Powell’s cell phone, Troyer said.

The house "lit up" about three minutes after the social worker was locked out, and it burned with a ferocity that prompted witnesses to believe the home had exploded, Troyer said. The social worker — who was not physically injured — called 911, then went to a neighbor’s home, Troyer said.

The three bodies were later found in the same room in the middle of the home, Troyer said.

Josh Powell’s death could mean that the disappearance of his 28-year-old wife Susan Powell from their West Valley City home in December 2009 will never be solved.

West Valley City Police Chief Thayle "Buzz" Nielsen, in an interview with KUTV 2, struggled to find words for the horror of what happened.

"This was just evil, this was a terrible thing," he said. "He wiped out the whole family. So selfish. Our guys are struggling through this. I don’t know, it hasn’t hit us yet."

Nielsen said he and other members of the department will be going to Washington for a strategy session with sheriff’s officers there.