GRAHAM, Wash. -- Gallons of gasoline spread throughout the home of Josh Powell caused the inferno that destroyed his home Sunday, authorities said Monday evening, but his two young sons, Charlie and Braden, also suffered from what investigators described as chop injuries to their heads or necks.

Autopsies on the three bodies were completed late Monday, confirming that the boys died as a result of homicide, and JoshPowell died as a result of suicide from carbon monoxide poisoning.

The Pierce County Medical Examiner confirmed Charlie Powell, 5, died of carbon monoxide poisoning, but a chop injury to his neck was a contributing factor. Braden Powell, 7, died in the same manner, but sufferred a chop injury to the neck and head.

Investigators recovered a hatchet that they believe was used on the boys.

Detectives called the explosion a deliberate, planned event in which two five-gallon cans of gasoline were used as an accelerant to blast the home apart; gas from one can was spread around the house, and the other can was apparently ignited in the center of the house, where the bodies of Josh, Charlie and Braden were found.

The house burst into flames after a social worker brought the boys there for a supervised visit. Powell blocked the social worker from entering the house.

Investigation shifts to Josh Powell's father

The Sunday blaze at Powell's home brought yet another twist in the very public scandal and investigation that began when Josh's wife, Susan Powell, vanished from the family's Utah home in 2009.

The investigation now shifts to Josh's father, Steven Powell, who is currently jailed on voyerism and child pornography charges and has refused to be interviewed since the explosion. Last fall, detectives found images and video of neighborhood girls, as well as Susan Powell, in his possession. Steven has been named a person of interest in her disappearance.

Susan's parents believe Steven Powell holds the key to finding out what really happened to their daughter.

I think he is the only one who would know. I think Josh would have confided in him enough to know where she might be, said Chuck Cox. He's not going to tell us anything.

It's up to the police, said Judy Cox.

Steven Powell claimed he and Susan had a romantic relationship, but detectives said Monday those statements are a flat out lie, and that Susan viewed her father-in-law as a creep, and weird.

Steven Powell has been put on suicide watch. Investigators have not said when they planned to speak to him.

Emails from Josh Powell found

Multiple emails from Josh Powell have since been found in close family members' in-boxes, including his cousins, and his pastor. Details of those emails have not been made explicitly clear, except that they included goodbyes and how to take care of any final business.

INTERACTIVE: Review the entire Powell case from the beginning

All of the emails were sent minutes before the social worker showed up at Powell's home with his sons Sunday afternoon for a court-ordered visitation.

Detectives said more evidence has emerged about Josh Powell's actions leading up to Sunday's blast, such as taking the boys' toys and books to Goodwill.

The deaths of Powell and the two boys brings an end to a case that started inDecember, 2009, when Josh's wife Susan went missing in the Utah desert. Her body has still not been found.

Attorneys for Susan's parents have said recently the boys had begun to talk about what happened the night their mother went missing, saying, Mommy was in the trunk. Josh maintained he and the boys went camping the night Susan disappeared, around 12:30 a.m.

However, detectives said Monday despite all of the evidence found so far at the scene, none of it has had anything to do with the disappearance of Susan.

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