By Breaking Celebrity News Staff

We've learned new details in the wake of the tragedy in Graham, Washington, where Josh Powell -- a person of interest in the two-year disappearance of wife Susan -- killed himself and his two young sons Sunday during what was to be a supervised visit with a social worker.

New overnight developments in the case reveal that Josh Powell had planned the home explosion that killed him for some time prior to Sunday; and even more shockingly, that the father murdered his two sons, 5-year-old Braden and 7-year-old Charles, with a hatchet prior to torching the home.