Before the fire erupted, the woman, who was supposed to monitor a supervised visit between Powell and his children, said he grabbed them and wouldn't let her in the door.
In the more than six-minute phone call, the social worker seemed to try repeatedly to relay the gravity of what was going on to dispatchers.
In the first minutes of the 911 call, the woman laid out the situation briefly, then asked, "What should I do? ... 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."
The dispatcher at one point asked the social worker what address she was at. The social worker didn't know and needed to look for it. It took her about 1 ½ minutes to find it in her car. At one point she asks, "You can't find me by GPS?" While she's still looking for the address she says, "But I think I need help right away."
The woman also explained that she smelled gasoline, saying four-minutes into the call that the boys have been locked in the home for 10 minutes.
After six minutes on the call, a dispatcher says: "We'll have somebody look for you there."
"OK, how long will it be?" the woman asks.
"I don't know ma'am. We have to respond to emergency life threatening situations first. The first available deputy."
The woman responded: "This could be life-threatening ... I'm afraid for their lives."
After the home erupted in flames, the woman screamed in a separate call: "He exploded the house!"
Also Tuesday, police searched a storage unit Powell rented as they tried to determine why he ultimately committed the murder-suicide, and questions remained about the status of the investigation into his wife's 2009 Utah disappearance.
For at least six months, Utah authorities have investigated the disappearance of Susan Powell as a murder case. But without a body, they publicly held out hope that she would be found alive.
What evidence did they have that the 28-year-old mother of two was dead? And was there anything to identify her killer?
There was the damp spot on the floor in the Powells' 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."
That could strike some as a clue, or the ramblings of a boy who was then just 2.
For authorities in Utah, none of it was enough to bring charges.
The man identified by investigators as a "person of interest" - Josh Powell - had already moved from Utah to Washington state, taking with him their two young sons. On Sunday, he torched his house, killing himself and the boys.
On Tuesday, investigators said Josh Powell withdrew $7,000 in cash from a bank the day before the deadly blaze. Police from Utah and Washington also searched a storage unit tied to Josh Powell in Pierce County, Wash.
Meanwhile a Washington state search warrant obtained by The Associated Press through a public records request showed that police were investigating three felonies in Utah since at least last summer: first-degree murder, kidnapping and obstructing a public servant.
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 AP that the case remains a missing persons probe for now.
Gill wouldn't discuss the evidence but said authorities had lacked enough information to file charges.
"I think when I talk about it as a missing persons case, that's because we haven't located the body of Susan Powell," Gill said. "Do we think that she may have met harm? Sure. I think that's been an ongoing assumption with law enforcement."
Josh Powell claimed that on the night Susan Powell vanished, he took sons Charlie and Braden from their home in West Valley City, Utah, on a late-night camping trip. Authorities eventually searched the central Utah desert but found nothing.
Susan Powell's father said that when police went to the family home after she was reported missing, they found a wet spot in the house being dried by two fans. Police have not commented further on what they found.
West Valley, Utah, Police Chief Buzz Nielsen said authorities needed concrete evidence to move forward.
"When you charge on criminal cases, especially if it ends up being a homicide ... without a body, it's just more difficult. You have to have a stronger case to make those arguments in court," Nielsen said. "We have circumstantial evidence that I'm not allowed to talk about it."
Last September, authorities got a warrant to search the Washington state home of Josh Powell's father, Steve. Josh Powell and his sons were living there at the time. The documents obtained by the AP did not specify a suspect.
In addition to the charges, the warrant listed Steve Powell's work laptop computer as well as cars that he used.
Authorities found explicit images on his computers during the search, and he was jailed on voyeurism and child porn charges. The boys were later sent to live with Susan Powell's parents.
Speaking to reporters after the boys' deaths, their grandfather Charles Cox said the boys were emotionally distant when they first arrived at their home but recently had begun to open up.
That gave Charles Cox hope that someday they would be able say what happened to their mom.
The boys had not recently made more comments about what may have happened to their mother, Charles Cox said, though he related what Braden said nearly two years ago.
Cox said: "The four ladies that were supervising that activity said, `Well, what's this?' `That's us going camping.' `Who's in the car?' And Braden said, `That's Daddy, that's Charlie, that's me.' Then he said, `Well, mommy's in the trunk.'
"Well if Mommy's in the trunk, why is she in the trunk?' He didn't know, he didn't say, I guess. Then, he said we stopped somewhere and mommy and daddy got out and mommy didn't come back," Cox said.
Nielsen said despite the death of the young boys and Josh Powell, the probe would continue.
"Our case is not closed," the police chief said.
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 person 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."
Anne Bremner, an attorney for the Cox family, said she believes there was enough circumstantial evidence to charge Josh Powell. And she said authorities had indicated in November that an arrest was near.
"There were a number of times where it looked as if there would be an arrest or a resolution, and it didn't happen," Bremner said. "And that was very frustrating to the family."