Josh Powell's family is not talking publicly about what happened Sunday, but we hear Powell himself in a recorded message he sent to his family shortly before killing himself and his boys.

NBCNews obtained what is believed to be the final voicemail left by Josh Powell minutes before he killed his two sons and himself Sunday.

This recording was reportedly left for Josh's brother, Michael, about 20 minutes before the murders.

Hello, this is Josh. And I m calling to say goodbye. I am not able to live without my sons, and I'm not able to go on anymore. I'm sorry to everyone I've hurt. Goodbye.

The boys' grandparents, Chuck and Judy Cox, who had custody of the children, don't think Josh sounded sincere in the recording.

He sounded distraught, but to say that he was couldn t go on without his kids, I think it was contrived. I mean he was distraught but it was contrived, that s why he s doing it, but he was planning this thing, said Chuck.

He has all along been saying what a good father he is and that he loves his kids more than anything and he would never hurt anyone. It just shows he's a liar, said Judy.

Another recording surfacing Tuesday gives insight into how firefighters learned about what happened in Graham Sunday.

Be advised there was explosions that occurred unknown if it was occupied or not. Could be a meth house. And we have P.D. responding.

Moments later dispatchers realized this was no meth house.

We have another caller on the phone that states that they believe there are two children and a father inside the residence.

The Pierce County Medical Examiner's office says Josh and the boys died of smoke inhalation, but the boys also suffered what authorities described as chop injuries to their heads or necks.

A Pierce County Sheriff s Department spokesman says investigators recovered a hatchet that they believe was used on the boys.

On Tuesday, investigators were searching Josh Powell's storage unit somewhere in the Puyallup area.

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

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.

Josh was also a person of interest in the disappearance of his wife, Susan Cox Powell, in Utah 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.

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