Autopsies are scheduled Monday for the boys, 5 and 7 years old, who were killed in a house explosion in Washington state on Sunday.
Authorities say they have no doubt the boys' father, Josh Powell, is responsible for the explosion that left himself and the boys dead.
The explosion erupted shortly after a social worker dropped off the two boys for a supervised visit.
Authorities say Powell locked the case worker out of the house before the explosion.
Powell reportedly wrote a short email to his attorney before the deadly fire. It read, "I'm sorry, goodbye."
Powell lost custody of the boys just days before the blast and police in Utah say they were building a case to charge Powell with the murder of his wife, Susan Powell, who vanished back in 2009.
Josh Powell was the only person of interest in Susan's case, but he had repeatedly denied any involvement in her disappearance.
After she vanished, police spent 12 days looking for clues in a Utah desert, 30 miles south of where Josh Powell told police he went camping with his two children in the hours before his wife's disappearance. This has been his steadfast alibi.
The lawyer for Susan Powell's parents told the AP on Sunday that the children had started talking to their grandparents about things they remembered from the night their mother vanished.
"They were beginning to verbalize more," said attorney Steve Downing, whose clients had custody of the children. "The oldest boy talked about that they went camping and that Mommy was in the trunk. Mom and Dad got out of the car and Mom disappeared."
Police found no clues in the Utah desert but a day after their search, Josh Powell's father, Steven Powell, was arrested at his Washington state home and accused of videotaping his daughter-in-law, other women, and young girls taking baths and sitting on the toilet in neighborhood homes.
The elder Powell is now jailed and facing child porn and voyeurism charges. He claimed in previous television interviews that he and Susan Powell were falling in love and even implied a sexual relationship had occurred.
Steven Powell was informed of the explosion on Sunday and is on suicide watch, said officials.
The Associated Press contributed to this report.