911 call made by social worker: Josh Powell 'Exploded the house!'

(CBS/AP) OLYMPIA, Wash. -- Authorities have released 911 tapes from the day Josh Powell set his house ablaze, killing himself and his two young sons.

The calls reveal a social worker's frantic attempts to alert authorities that Powell had locked himself and his kids in his home moments before the huge fire.

PICTURES: Missing Utah Mother Susan PowellPICTURES: Missing Utah mom's kids, husband die in alleged murder-suicide

"He exploded the house!" The social worker tells a dispatcher.

Before the blast, Elizabeth Griffin-Hall, who was there to monitor a supervised visit between Powell and his boys, said he grabbed them and wouldn't let her in the door.

"What should I do?" she asks the dispatcher. "Something really weird has happened. I'm really shocked, nothing like this has ever happened before at these visitations...I could hear one of the kids crying and he still wouldn't let me in."

Griffin-Hall then begins to sense danger and pleads with a 911 operator to send someone quickly.

"I'd like to pull out of the driveway because I smell gasoline, and he won't let me in," Griffin-Hall says.

Inside the house, Josh Powell is brutally attacking his children with a hatchet.

Griffin-Hall then asks how long it will be until help arrives and the dispatcher tells her they have to respond to life-threatening situations first.

"This could be life-threatening," Griffin-Hall stresses. "He went to court on Wednesday and he didn't get his kids back and this is really -- I'm afraid for their lives."

Moments later, Powell torches the home as an explosion shakes the neighborhood.

"Yes, he exploded the house!" Griffin-Hall cries out. "He exploded the house. He blew up the house and the kids!"

"The kids and the father were in the house?" the dispatcher asks.

"Yes," says Griffin-Hall. "He slammed the door in my face. So I kept knocking. I thought it was a mistake, I kept knocking, and then I called 9-1-1."

Authorities still do not know what happened to his missing wife, Susan Powell, who disappeared in Dec. 2009, when the family lived in Utah.

Tuesday, police searched a storage unit Powell rented as they tried to determine why he ultimately committed the murder-suicide. Questions also remain about the status of the investigation.

Police has only a few inconclusive clues. There was a damp spot on the floor in the Powell's Utah home and a curious late-night camping trip described by Josh Powell. There were also the recollections of their young son Braden about a camping trip and his mother being "in the trunk."

For police in Utah, none of it was enough to bring charges against the "person of interest" Powell.

Salt Lake County District Attorney Sim Gill acknowledged for the first time that investigators believe Susan Powell is likely dead but he said in an interview with the Associated Press that the case remains a missing persons probe for now.

Pierce County Prosecutor Mark Lindquist, who is overseeing the voyeurism prosecution of Steve Powell but is not directly involved in the Susan Powell case, said it's clear to him that it's a homicide case.

"I don't think at this point I'm going to call this a missing persons case," he said. "It's reasonable to call Josh Powell's decision to kill himself and his kids a confession to the murder of Susan Powell."

Complete Coverage of Susan Powell on Crimesider