Pierce County sheriff's spokesman Ed Troyer accused Josh Powell, a suspect in his wife's disappearance in Utah in 2009, of intentionally setting the fire in Puyallup, Wash., that caused an explosion Sunday, killing him and his sons, Braden, 5, and Charlie, 7, CNN reported Monday.
"This was all on him," Troyer said, accusing Powell of murder-suicide. "He set this up. He did it."
The sheriff's department has copies of the e-mail Powell sent to his attorney, family members and friends in which he said "he couldn't live with what was going on," Troyer said.
The e-mail to the attorney read: "I'm sorry. Goodbye."
Although a medical examiner hasn't definitively identified the bodies, the sheriff's spokesman said "we believe it is the three of them."
"This was something that was done deliberately and intentionally, and the plan was carried out very quickly," Troyer said.
Powell's wife, Susan Powell-Cox, has been missing for more than two years and Powell has been engaged in a custody dispute with his wife's parents. The children were moved to Cox's parents' home after authorities found pornography in the home of Powell's father, Steven Powell, where he and his sons were living, CNN said. Steven Powell was arrested and eventually charged with voyeurism and possessing images of children engaged in sexually explicit conduct, court documents indicated.
A judge's refusal of Powell's petition to regain custody of his boys and ordering him to undergo psychological evaluations apparently was the trigger for Sunday's events, the sheriff's office said.
Authorities said Powell waited outside his home for a social worker to bring his boys for a supervised visit, authorities said. As the children reached the door, Powell shoved the social worker back, took his sons inside and locked the door.
The social worker, who reported smelling something akin to gas, tried "pounding the doors, trying to get in," said Gary Franz, a deputy chief with Graham Fire and Rescue.
While she was calling her supervisor the house exploded, rattling windows and shaking nearby homes, Franz said.
In Utah, a relative said Powell's act was an "admission of guilt," KUTV, Salt Lake City reported.
"I think this is his admission of guilt, and he just couldn't handle it anymore," Kirk Graves, Powell's brother-in-law, told KUTV, Salt Lake City.